Procedural Polarization in the U.S. Congress

Procedural Polarization in the U.S. Congress*

                                         Sean M. Theriault
                                The University of Texas at Austin
                                      seant@mail.utexas.edu

                                         February 21, 2006

        This article examines party polarization in Congress. It finds that almost the
        entire growth in party polarization since the early 1970s can be explained by
        the increased frequency of and polarization on procedural votes in the both the
        House and the Senate. This finding answers several questions about party
        polarization, but asks one new questions that it only begins to answer: what
        are procedural votes? Preliminary analysis suggests that members of
        Congress view procedural votes as separate and distinct from substantive
        votes. On the former, their party has a substantial influence on their behavior
        and on the latter, their constituency has a substantial influence.

      Paper prepared for presentation at the American Political Development Workshop
                            Madison, Wisconsin, March 24, 2006.

*
 The author gratefully acknowledges helpful comments and careful criticisms from Jonathan Bendor,
Mo Fiorina, Jonathan Katz, Keith Krehbiel, Simon Jackman, and Barry Weingast as well as engaging
audiences at the Hoover Institute at Stanford University, the Junior Faculty Seminar at the University
of Texas, and the University of Nebraska.

Theriault                                            2

         The atmosphere on Capitol Hill is poisonous. Members from the opposing political
parties are at each other’s throats. In the wake of his reelection as president, Bill Clinton
thanked the American public for turning back “the politics of personal destruction,” a phrase
that became a political moniker for the late 1990s.1 Since then, it not only describes the
campaign strategies of the parties during elections but also the governing strategies in
between elections. Almost 6 years later, when Robert Torricelli withdrew from his Senate
reelection race as a result of compelling evidence involving financial impropriety, he feared
that the politicians’ animus had infecting the populace. He asked: “When did we become
such an unforgiving people?”2
         A precise answer to Torricelli’s question is beyond the scope of this article. The
conditions that gave rise to the “politics of personal destruction” and an “unforgiving
people,” however, probably have their roots in the heated political debates of the 1960s.
After the insurgent Republicans brought down Speaker Cannon in 1910, the parties
converged to such an extent that sociologist Daniel Bell wrote a book titled, The End of
Ideology, in 1962, and George Wallace did not see a dime’s worth of difference between the
parties in the 1968 presidential election. But, by the early 1970s, Democrats and
Republicans in both chambers began casting more internally homogenous and externally
heterogeneous votes, which reversed a trend of party convergence that dominated the
twentieth century (Turner 1970, Coleman 1997, Rohde 1991, Stonecash et al. 2003, and
Theriault 2003).
         The trend of increased party voting begun in the 1970s has continued almost without
restraint. Indeed, it is a common chorus in the congressional literature these days. Fleisher
and Bond (2004, 429) analyze “the virtual disappearance of moderate and cross-pressured
members from the U.S. Congress.” Stonecash et al. (2003, xiii) find, “The parties
increasingly adopt sharply differing policy positions. Democrats have more liberal voting
records than they did thirty years ago, and Republicans have more conservative voting
records. Party conflict is pervasive in the House.” Theriault (Forthcoming,1) adds, “The two
political parties in Congress are as ideologically distant as they have been at any point in the
last three decades.”3
         As evidenced by these quotes, party polarization is one of the most recognizable and
persistent trends in American politics over the last 30 years. As a profession, it is in our
blood to be disagreeable, but what everyone in the congressional literature seems to agree
upon is that party polarization between Democrats and Republicans in Congress is growing.
At the outset of this article, I ask the reader to suspend that agreed upon notion that the
parties are diverging. I am not so foolish to suggest that the parties have not diverged, just

1
  The first appearance of “the politics of personal destruction” phrase in a major newspaper was on
November 6, 1996, in the article, “Clinton Wins Big,” written by Douglas Turner for The Buffalo
News, p. 1A.
2
  Quoted in “In His Own Eulogy, A Senator Unbowed: Torricelli Recites Litany of Accomplishments
During 20-Year Political Career,” Washington Post, October 1, 2002, p. A4.
3
  See also Aldrich 1995, Coleman 1987, Collie and Mason 2000, Fiorina 1999, Fleisher and Bond
2000, Jacobson 2000, Roberts and Smith 2003, Rohde 1991, and Sinclair 2000a.

Party Polarization in Congress                                       3

that this polarization is overblown.4 When individual, micro-level data are analyzed, we find
that the substantive divide at the elite level is more illusory than real. In fact, almost the
entire growth in party divergence since the 1970s can be explained by the increasing
frequency of and polarization on procedural votes in both the House and Senate.
        In exploring party polarization, this article answers some questions, but raises many
new ones. In the first section, I describe the state of party polarization as currently described
in the congressional literature. The second section explores a conundrum of the party
polarization literature. The favored explanation for party polarization – the districting-based
explanations of redistricting, political sorting, and ideological migration – only accounts for
about 25 percent of the total party polarization in the House and about 5 percent of the party
polarization in the Senate. In the third section, I dig deep into the individual votes of
members to Congress to show that procedural votes by and large explain the increase in party
polarization over the last 30 years. The fourth section speculates about the meaning behind
these procedural votes. Preliminary evidence suggests that majority parties are using
procedures increasingly to hardwire substantive outcomes. The fifth section concludes.

I. The Polarized Congress

        Because the polarization between the legislative parties has been described effectively
by a number of scholars (see, for example, Aldrich 1995, Coleman 1997, Collie and Mason
2000, Fiorina 1999, Fleisher and Bond 2000, 2003, Jacobson 2000, Roberts and Smith 2003,
Rohde 1991, Sinclair 2000a, and Stonecash et al. 2003, Theriault Forthcoming), this section
provides only the bare minimum to motivate the casual reader and to remind the forgetful
reader. In the early 1970s, the parties were as ideologically similar as they had been since
the Civil War (Theriault 2003). The difference between the means for the Democrats and
Republicans on the DW-NOMINATE scale in the 93rd Congress (1973-4) in both the House
and the Senate was 29 percent. Over the next 32 years the parties became more distinct, such
that the division between them in the 108th Congress (2003-4) was 43 in the House and 38 in
the Senate. The polarizing trend is: (1) highly correlated between the House and Senate
(0.98; p=0.00), (2) present in both the North and the South, though the South has gone from
being less polarized than the North to being more polarized, (3) a consequence of both
member replacement and adaptation (Fleisher and Bond 2004 and Theriault Forthcoming),
and (4) not dependent upon DW-NOMINATE scores.5
        My own measure – party disparity scores – confirms these four accepted conclusions.
To compute party disparity scores, I subtract the absolute difference between the percentages
of Republicans and Democrats who vote the same way on roll-call votes. For example, if all

4
  In this sense, this article follows the work of Snyder (1992), who finds that interest groups ratings
are artificially extreme as a consequence of incorporating a higher proportion of closely decided roll-
call votes.
5
  Different scholars using different methods show the same basic pattern by analyzing different data
including: party votes (Coleman 1997 and Stonecash et al. 2003), party unity scores (Coleman 1997,
Rohde 1991, and Stonecash et al. 2003), Americans for Democratic Action (ADA) scores (Taylor
1996, Stonecash et al. 2003), American Conservative Union (ACU) scores (Collie and Mason 2000),
and a mixture of ADA and ACU scores (Fleisher and Bond 2000). Shipan and Lowry (2001) even
show how the parties have diverged in a particular policy area.

Theriault                                              4

legislators voted together or if exactly half of the Democrats and half of the Republicans
voted to pass a bill, the party disparity measure would be 0. If every Democrat voted against
every Republican the measure would be 1. If 60 percent of Democrats sided with 90 percent
of Republicans or vice versa, the party disparity measure would be 30 percent (the absolute
difference between 90 percent and 60 percent). Averaging across roll-call votes from the
same congress results in a congress’s party disparity score.6 I use three different databases to
compute the party disparity scores. First, I use Rhode’s (2005) data set of all 17,492 roll-call
votes in the House from 1973 to 2004. Second and third, because the issues that may be
resolved on the House floor might have changed over time and to provide for analysis on the
Senate, I analyze the 2908 House and 4120 Senate roll-call votes on the 609 most important
pieces of legislation, as designated by Mayhew (1991, 2005) and Edwards et al. (1997,
2000), from 1973 to 2004.7 The party disparity average trends for the three databases show
that they act similarly over the last 32 years (see figure 1).8 Because each shows more
polarization than the DW-NOMINATE scores, party disparity scores provide a difficult test
for the conclusion that substantive polarization is overblown.
Insert Figure 1.

II. Moderate Electorates and Polarized Legislators

        The accuracy with which different methodologies and different data yield similar
party polarization results suggests that it is a real phenomenon in American politics. Even
scholars who question the existence of party polarization in the mass electorate admit that the
political elites have indeed polarized. On the other hand, scholars who argue that the
electorate has polarized readily admit that the elites have polarized to an ever greater extent.
The literature has been more comprehensive in investigating the extent to which the
electorate and the elites have polarized than it has been in linking the two phenomenon
together.
        Morris Fiorina (1999) asked the question most explicitly in the title of a paper
delivered at the Midwest Political Science Annual Meeting: “What Ever Happened to the
Median Voter?” In the paper, he speculated about how it is that a mass population that is
moderating could possibly elect a legislature that is polarizing. That argument was fleshed
out and presented more formally in the 2005 (updated in 2006) book entitled Culture Wars?
Fiorina’s penultimate chapter attempts to reconcile the concurrent trends of a moderating
electorate and a polarizing Congress. Fiorina’s analysis shows how various electoral
practices and procedures have led increasingly to elections between a liberal candidate and a
conservative candidate. In Fiorina’s (2006, 169) words: “Given a choice between two
extremes, they [the voters] can only elect an extremist.”

6
  The computation of the party disparity measure is the same as Turner’s (1970, 42) “index of
likeness, except that he subtracts the disparity measure from 100 to arrive at his likeness score.
7
  Mayhew updates his list every Congress. The most important legislative enactments can be found
at: http://pantheon.yale.edu/~dmayhew/data3.html. Using Edwards’ methodology, I updated his list
of major failures. The list can be downloaded at: http://www.la.utexas.edu/~seant/failure.html.
8
  Additionally, they are highly correlated with one another (0.85; p=0.00) and DW-NOMINATE
scores (0.89 for procedural votes and 0.85 for substantive votes; both p=0.00).

Party Polarization in Congress                              5

         In an answer to Fiorina’s initial questions, the literature has decided that even if the
American electorate in total has not polarized, members’ constituencies have polarized. As
they have polarized, they have elected more ideological members. Some scholars point to
partisan redistricting as the culprit (Carson, Crespin, Finocchiaro, and Rohde 2004). Norman
Ornstein (2004, 7) wrote, “Congressional redistricting…has eliminated most competitive
seats and thus removed most centrists and moderates from both parties.” Hirsch (2003, 215)
offers a more rigorous criticism: “But today, a handful of congressional and state-legislative
leaders pursuing a narrow partisan and ideological agenda are threatening to transform what
should be our most democratic institution into something sclerotic and skewed.” Other
scholars argue that the polarization of constituencies has happened more organically as voters
have sorted themselves into the appropriate political parties and migrated to live in like-
minded neighborhoods. Hetherington (2001), Galston and Kamarck (2005), and
Abramowitz, Alexander, and Gunning (Forthcoming) show that voters’ ballots are more
consistent with their ideology. Bishop (2004), Oppenheimer (2005), Gimpel and Schuknecht
(2003) and Giroux (2005) show how migration patterns complimented and bolstered the
sorting of voters into more homogenous political jurisdictions.
         The combined effect of these two trends has powerful consequences. In analyzing
not only districts’ partisanship but also some of their underlying demographics, Brewer,
Mariani, and Stonecash (2002) and Stonecash, Brewer, and Mariani (2003) show that
increasingly over time, Democrats represent poorer and more ethnically diverse districts than
Republicans. Additionally, McCarty, Poole, and Rosenthal (Forthcoming) show how the
income inequality of the constituencies of Democrats and Republicans has exasperated the
substantive party differences. Policy disagreements and polarization, according to this
argument, follow the trend that each party’s constituency base has become increasingly
internally homogenous and externally heterogeneous. Bryan Jones, quoted in a Seattle Times
story, nicely summarizes the argument: “Lawmakers elected from solidly safe districts have
less incentive to compromise… Homogenous districts add to the polarization of the political
parties.”9
         Not only is the logic of the constituency-based explanations of redistricting, political
sorting, and ideological migration compelling, but there is growing evidence to substantiate
it. Most simply, the constituencies represented by the respective party caucuses are
increasingly polarized. In the 93rd Congress (1973-4), Republicans in the House represented
districts that gave Nixon, on average, 5 percent more of the two-party vote than Nixon
received nationwide. Democrats, on the other hand, represented districts where Nixon got 4
percent less of the two party vote than he did nationwide. This 9-point disparity arising from
the 1972 election more than doubled to 19 percent after the 2000 election. Figure 2 shows
the trend of these numbers over time. The disparity in the Senate increased even more. In
the 93rd Congress, Republicans came from states where Nixon did 1 percent better than he
did nationwide. Democrats came from states where Nixon did 1 percent worse than he did
nationwide. This 2-point disparity tripled to 6 percent in the 2000 elections. Put simply, the
divide between Democrats’ and Republicans’ constituencies, in both the House and Senate,
was at least twice as much in the early 2000s as it was even 30 years before.
Insert Figure 2.

9
 Quoted in David Postman, “Why So Many Races Lack One Thing: Competition,” The Seattle
Times, October 13, 2002, p. A1.

Theriault                                             6

         The underlying assumption of the constituency-based explanations requires that
ideologically purer constituencies elect ideologically purer members. To evaluate this
argument, I divide members into two groups based on their constituencies’ “corrected”
Democratic presidential vote advantage. Democratic members that represent constituencies
that gave Democratic presidential candidates more than 5 percentage points more than the
candidates’ national average are classified as coming from “strong” districts or states.
Members representing constituencies that gave the Democratic presidential candidates less
than 5 percentage points above their national average are classified as coming from “weak”
districts or states; likewise for Republicans.
         Ted Kennedy is the prototype of a senator in the first category. His party, Democrat,
is the same as the partisanship of his state, Massachusetts. Kent Conrad of North Dakota
represents the classic weak state. Although a Democrat, his state regularly votes for
Republican presidential candidates. Even though Conrad’s lowest victory margin since his
first reelection in 1992 was 16 percentage points, the highest percentage that a Democratic
presidential candidate got since then was Clinton’s 40 percent in 1996. The division based
on the constituencies’ partisanship permits a distinction between the polarization brought
about by the homogenization of members’ constituencies and the polarization brought about
by members’ polarization scores controlling for their constituencies.
         The number of members and senators coming from safe constituencies has increased
over time. Panel A of figure 3 shows that by the 99th Congress (1985-6), the number of
members coming from safe districts exceeds the number of members coming from weak
districts. By the 108th Congress, almost twice as many members came from safe districts. In
the Senate (panel B), the lion’s share of the senators serving in the 1970s and 1980s came
from weak partisan states. Over time, the disparity between categories shrinks, such that by
the 108th Congress almost as many senators came from safe states as weak states.
Insert Figure 3.
         The next step requires that the members from these safer constituencies vote more
ideologically than the members from weak constituencies. Consistent with the hypothesis,
representatives (senators) in the safest districts (states) went from a 0.36 (0.36) polarization
score in the 93rd Congress to 0.48 (0.44) in the 108th Congress.10 But, somewhat
unexpectedly, the members from the weakest districts also became more polarized over time
(see figure 4). Representatives (senators) in the weakest districts increased from 0.24 (0.27)
to 0.33 (0.33).
Insert Figure 4.
         The evidence from this analysis suggests that both steps of the constituency-based
assumption are valid: the constituencies of members have become more partisan and more
partisan constituencies have elected more ideological members. But what this evidence does
not show is the magnitude of these effects on the overall party polarization. To determine
how responsible the members’ constituencies are in polarizing the Congress, I conduct
counterfactual analysis, first holding the average polarization scores across time constant and
varying the frequency of the members within the safe and weak categories and then holding

10
  These polarization scores are computing using DW-NOMINATE scores. First, Democrats’ scores
are multiplied by -1 so that they are on the same scale as Republican members. Second, all the scores
within the categories are averaged to arrive at the reported polarization score.

Party Polarization in Congress                               7

the frequencies across time constant while varying the average polarization scores within
categories. If the ideology of the representatives in the two categories did not change, the
House would have been only 3 percent more polarized in the 108th Congress (2003-4) than it
was in the 93rd Congress (1973-4). This suggests that the polarization brought about by
constituency change is only about 3 percentage points more than it was in the 92nd Congress.
By both categories becoming more polarized, the polarization of the House grew by 10
percentage points, implying that the fact that all members have become more polarized above
and beyond the constituency change accounts for a 10 percentage point increase in the
polarization since the early 1970s. In total, the growing ideological separation between the
parties controlling for the more partisan constituencies has caused 77 percent of the House
polarization over the last 30 years (see panel A of figure 5). Only 23 percent of the House
polarization was caused by the increasing partisanship of the representatives’ constituencies.
Insert Figure 5.
        The parallel analysis for the Senate (see panel B of figure 5) is even more one-sided
than the House. If the polarization score did not change within the individual categories and
only the number of senators from strong and weak states changed, the Senate in the 108th
Congress would have been only about 1 percentage point more polarized than it was in the
92nd Congress. If the number of senators within categories did not change and only the
polarization score within categories changed, the Senate in the 108th Congress would have
been 21 percentage points more polarized. These figures suggest that less than 5 percent of
the polarization in the Senate is caused by the states’ growing partisanship. Senators’
increased ideological voting above and beyond the growing ideological polarization of their
constituencies brought about the remaining 95 percent of the polarization. These relative
assessments suggest that the increased political segregation of members’ constituencies does
have a definite impact on congressional polarization, though, probably a smaller impact than
its proponents suggest.

III. Procedural versus Substantive Polarization

        In this section, I resolve the trends from figure 1 with the conundrum raised in the
previous section. I find that almost all of the increase in party polarization is a consequence
of an increasing frequency on and an increasing polarization of procedural votes in the House
and the Senate. Before demonstrating these trends, I first show how the House and the
Senate have become a increasingly procedural places.

Restrictive Rules in the House of Representatives
        During the 1994 congressional elections, the Republicans promised to restore
democracy to the House of Representatives if they became the majority party by opening up
the floor to more open rules. They pointed to the increasing number of closed and restricted
rules as a sign of the Democratic leadership’s arrogant use of power. They vowed that more
bills would enjoy open rules under a Republican-led House. True to their word, the
percentage of bills that received an open rule almost doubled from 30 percent in the 103rd
Congress (1993-4), the last one in Democratic hands, to 57 percent in the 104th Congress
(1995-6), the first one in Republican hands (see figure 6A). Since the 104th
Congress, however, the percentage of restrictive rules has climbed such that by the 108th

Theriault                                              8

Congress (2003-4) the Republicans used a higher percentage of restricted or closed rules than
the Democrats ever did. Panel B shows the proportion of restrictive rules on the 609 most
important pieces of legislation since the 93rd Congress (of which only 290 had House rules).
Although the first few Republican congresses had more open rules than the last few
Democratic congresses, the 107th and 108th (2001-2004) did not have any open rules at all on
major legislation.
Insert Figure 6.

Complex Unanimous Consent Agreements in the Senate
        xx-This section will show that the UCAs have become much more complex over the
last 30 years.

Party Disparity on Procedural, Amendment, and Substantive Votes
        To measure the impact that increasingly structured floor proceedings in the House
and the Senate have had on party polarization, I analyze the party disparity scores from all
17,492 House votes and the 7,028 roll calls from the House and Senate on the 609 most
important pieces of legislation since 1973. Each roll call is classified as a procedural, an
amendment, or a substantive vote. Procedural votes establish the format, topic, and manner
of debate. They include votes on motions to order the previous question, special House rules,
motions to recommit, motions to instruct conferees, and cloture motions. The amendment
category includes straightforward votes on amendments as well as second degree
amendments and motions to table amendments. Substantive votes decide the final resolution
of policies. They include votes on final passage, votes on the adoption of conference
committee reports, and votes to override presidential vetoes.11
        The frequency trend of the vote types is visually represented in figure 7 and is
characterized in table 1A. Although figure 7 shows a certain amount of instability in the
frequency of different kinds of votes for all House votes (panel A) and votes on the most
important pieces of legislation in the House (panel B) and the Senate (panel C), its
characterization by a time trend in the regression results in table 1 more easily shows the
trends over the 16 congresses from the 93rd to the 108th (1973-2004). The only one of the
vote types that increases in all three datasets is procedural votes. The time trend for
amendment and substantive votes in all three datasets has a negative coefficient, though they
never reach conventional levels of statistical significance.
Insert Figure 7.

Insert Table 1.

11
   Because of their overall importance, various scholars examine only final passage votes in testing
their arguments about the process (see Jenkins, Crespin, and Carson 2003, Thorson 1998, Cox and
McCubbins Forthcoming, and Krehbiel, Meirowitz, and Woon 2005). Krehbiel and Woon (2005)
criticize this approach because, as a summary of member behavior, it both excludes other important
votes and includes largely irrelevant votes. My approach is subject to this criticism, but less so
because I am more interested in the difference in voting on substantive votes (largely comprised of
final passage vote) and procedural votes. Additionally, I test the argument on all substantive votes as
well as the substantive votes on only the most important pieces of legislation, which reduces the
errors associated with the inclusion of irrelevant votes.

Party Polarization in Congress                                 9

         Froman and Ripley (1965) first point out the difference in voting on procedural and
substantive matters in votes from the early 1960s.12 Tuner (1970) embeds their logic and
findings in a longer study. He finds drastic differences in party voting on procedural matters
in roll calls from 1921 to 1964. Rohde (1991), Ansolabehere, Snyder, and Stewart (2001),
and Cox and Poole (2002) find that the current congressional setting extends and exacerbates
the findings from these earlier studies. My findings nicely dovetail these later results. The
polarization on all three categories of votes has risen, though its rise has been most dramatic
on procedural votes (see figure 8 and table 1B). Among all House votes, procedural votes
became 3 percentage points more polarizing each congress, whereas amendment votes
became 1.5 percent and substantive votes became 0.4 percent more polarizing each congress.
These same relationships are played out when the votes are restricted to the most important
pieces of legislation in the House and the Senate. Disparity in party voting increased in all
vote type categories, but it increased the most on procedural votes.
Insert Figure 8.
         The combination of the two trends depicted in figures 7 and 8 reveals the true impact
that procedural votes have had on party polarization in the U.S. Congress since the early
1970s. Figure 9 shows the responsibility of each of the vote types on party disparity scores
from the 93rd to the 108th Congress (1973-2004), and table 1C characterizes the trend. With
each passing congress, the chambers became between 1.1 and 1.8 percent more polarized as a
consequence of the increasing frequency of and polarization on procedural votes. In
comparison, substantive votes have increased the polarization between 0.03 and 0.3 percent
each congress, which is at most one-sixth as much as procedural votes. Although
amendment votes have polarized the House about as much as substantive votes, they
polarized the Senate almost as much as procedural votes.
Insert Figure 9.

IV. Understanding Procedures in the U.S. Congress

        Substantive votes have caused less than one-fourth of the party polarization on all
House Votes, less than one-sixth of the party polarization on the most important legislation
votes in the House, and less than one-twelfth of the party polarization on the most important
legislation votes in the Senate. The party polarization trend is not driven by these relatively
minor increases in polarization on substantive votes in the House or the Senate. But for the
increasing frequency of and polarization on procedural votes, few political scientists would
have even recognized the trend of party polarization and none of them would probably have
bothered to try and explain it.
        These findings only beg the question: What are procedural votes and what explains
their effect on party polarization? This section outlines three possible answers. The first
potential answer is tested individually. Due to the nature of the second and third answers,

12
  Froman and Ripley (1965) develop 7 categories of votes and align them on a procedural to
substance continuum. Their categories are highly correlated, though not perfectly, with my three
categories of votes. The biggest disparity is on recommittal motions, which Froman and Ripley place
toward the substantive end of their continuum (after only amendment and conference committee
report votes).

Theriault                                         10

they are tested against one another. Before continuing to the tests, I should note that this
section does not explicit consider amendment votes. The results on amendment votes, like
the results presented above, are halfway in between the results for procedural and substantive
votes.

Close Margins Hypothesis
         The first explanation for the increasing use of procedure in the House and Senate has
its roots not in party polarization, but in the margin between the parties’ memberships in the
respective chambers. According to this argument, as the number of minority party members
approaches the number of majority party members, the majority party is forced to accomplish
more procedurally in order to win substantively. Because as the majority party adds to its
majority it is more likely to win substantively, it need not put in place strict procedures to
ensure substantive wins. As Dion (2001, 245) nicely summarizes in the conclusion of his
book on minority rights: “Small majorities are more cohesive, cohesive majorities lead to
minority obstruction, minority obstruction leads to procedural changes on the part of the
majority to limit obstruction” (see also, Binder 1997, 2005). At the end of the day, close
margins cause partisan procedural moves, which cause party polarization.
         If the close margins argument is correct, the number of minority party members
should be positively correlated with procedural polarization. Initial evidence seems to
indicate that the margin hypothesis has some validity. The correlations among the number of
minority party members, procedural polarization, and the share of polarization that is
procedural easily achieve standard levels of statistical significance in the House and are or
are near statistical significance in the Senate. For every additional member that the minority
party has in the House, procedural polarization increases around 0.4 percent and the share of
polarization that is procedural increases more than 0.1 percent. For every additional senator
the minority party has, procedural polarization increases 3 percent and the share of
polarization that is procedural increases almost 1 percent.
         Concluding that the close margin hypothesis is correct based on this initial analysis
would be hasty. When the correlations are controlled for time, they completely wash away.
In fact, the coefficient on the number of minority party member’s variable in every case turns
negative, though none achieve statistical significance. This more complex analysis suggests
that the minority party membership variable in the first set of results is acting as a proxy for a
time trend variable. Indeed, the correlation between minority party membership and the time
trend is 0.72 (p=0.002) in the House and 0.68 (p=0.004) in the Senate.

Divisive Procedures Mask Substantive Disparity Hypothesis
        The second explanation for the increasing use of and polarization on procedural votes
argues that disparity in substantive voting is masked through divisive procedures. If
members know that through procedures, substantive outcomes can be hardwired, they will
shift the subject of the debate from substance to procedures. Proponents of this argument
would reject the vary notion of labeling a vote “procedural.” Because any procedural vote
has substantive affects, members consider the substantive impact when they cast this
“procedural” vote. As Froman and Ripley (1965, 56) pointed out over 40 years ago, “Most
votes, of course, involve both procedural and substantive questions. Even a motion to
adjourn can sometimes be partly a substantive issue, if the motion is directed at postponing
action on a bill.”

Party Polarization in Congress                               11

         This explanation has its roots in Robin Farquharson’s (1969) seminal book, Theory of
Voting, which shows how the procedures surrounding a sequence of votes affects the voters’
ultimate decisions. Using his logic, Riker (1986, ix) developed the name “heresthetic” to
describe the study of “structuring the world so you can win.” “Agenda control,” which
procedures establish is according to Riker (1986, 130), “a concentration of the opportunity
for heresthetical manipulation.” But, Riker (1986, 140) warns, “Heresthetical resources of
parliamentary leaders are entirely dependent on a supportive majority.” Denzau, Riker, and
Shepsle (1985, 1118) show how heresthetics work in the legislature: “Result- or outcome-
oriented legislators should regard the alternatives on the floor at any stage of the voting
process (but the last) not as objects of choice per se, but rather as vehicles that carry the
process into the next stage of the sequence.” This argument assumes that members are
forward looking and sophisticated enough to understand that by adopting certain procedures
in a bill’s debate, they are significantly affecting their ability to substantively alter the bill’s
language. Furthermore, Krehbiel and Meirowitz (2002) show that through the use of the
most procedural of motions, the motion to recommit, the minority party can substantively
check the majority party at the penultimate stage of the legislative process in the House.
         This same literature also provides a hurdle for the procedural-as-substance argument.
Denzau, Riker, and Shepsle (1985, 1125) demonstrate how constituent pressure can break
down that argument: “Congressmen do not like to debate parliamentary counterfactuals with
their opponents, and generally seek to avoid votes necessitating complicated explanations. In
this light, strategic voting begins to look less compelling.” They mention that even forward-
looking and intelligent members may be hard pressed to act thoughtfully and sophisticatedly
when their constituents and future potential challengers are watching their every move.

Parties Care about Procedures; Constituents Care about Substance Hypothesis
        The third explanation argues that the increasing frequency of and polarization on
procedural votes has its roots in the power exercised by party leaders (Rohde 1991, Aldrich
1995, Aldrich and Rohde 2001, Ansolabehere, Snyder, and Stewart (2001), and Cox and
McCubbins Forthcoming). Party leaders, who are primarily concerned with the outcome of a
substantive vote, establish the best possible set of procedures to arrive at their preferred
substantive outcome. The leaders use procedure to hardwire the final outcome because they
assume that they can more easily obtain support from their partisans on procedural matters.
As Jones (1968, 618) explains:
        Substantive majorities are those necessary to pass legislation in the House. Whereas
        procedural majorities may well differ issue to issue, since many substantive measures
        cut across party lines. Leaders are expected to build substantive majorities—
        employing the many bargaining advantages provided by their procedural majorities.
        They are not expected, nor do they normally have the power, to force members into
        substantive majorities.
Proponents of this explanation point to three powers in the party leaders’ arsenal that helps
them to encourage party voting on procedures.
         First, party leaders have more control over not only the legislation brought up on the
chambers’ floors, but also the manner in which the legislation is debated. The frequency of
restrictive rules and the increasing use of complex unanimous consent agreements are the
most obvious example of how they have exercised this power. Party leaders can also hinder
or propel legislation by placing it in privileged or disadvantaged positions in the calendar
(Jenkins, Crespin, and Carson 2005).

Theriault                                       12

         Second, party leaders have increasing control over campaign resources. In the 1987-
8, the congressional campaign committees for both parties in both chambers had $129
million in receipts. In the 2003-4 cycle, they had access to almost two and one-half times
that much ($447 million). This increase in campaign resources looks minor when compared
to the total amount that members’ leadership PACs have received and distributed over the
same time period (Pearson xx and Kolodny 1998). Leaders can use these campaign
contributions to entice loyalty among their members or to help members who have cast loyal
votes fend off aggressive challengers.
         Third, party leaders have more discretion in the naming of not only committee
members, but also committee leaders. Through a series of reforms begun by the Democrats
in the early 1970s and continued by the Republicans in the 1990s, committee positions are
now more a function of how the members are viewed by the party leadership rather than the
age-old seniority system. As an indication of how the latter has collapsed in the face of the
former, the Republican party leaders since they became the majority in 1995 have refused to
give the committee chair job to the most senior Republican on the committees 14 times,
instead naming a more loyal Republican leadership team player to the position (Pearson
2005). Ten of these seniority violations occurred in the 107th and 108th Congresses.
         These increases in party leader power either have their origins in or have been
exacerbated by a series of institutional reforms such as the Budget Act of 1974, which
centralized fiscal decision-making in Congress; the establishment of multiple referrals; the
increasing use of special rules on the House floor; the centralization of the committee
assignment process; the increased inventiveness of Senate rules and procedures by party
leaders during floor deliberations; the decreased autonomy of the Rules Committee; the
creation of task forces to bypass committees; and the revitalization of the speaker’s powers
(Schickler 2001, Aldrich 1995, and Sinclair 2000b). Perhaps more important than these
institutional changes is the sorting out of the constituencies (Abramowitz, Alexander, and
Gunning 2006 and Stonecash, Brewer, and Mariani 2003), which has provided the incentives
for rank and file members to give more power to their party leaders (Rohde 1991, Aldrich
1993, and Aldrich and Rohde 2001). In fact, Theriault (2006) argues that it is the
increasingly polarized constituencies that have encouraged the rank and file party leaders to
grant more power to their party leaders. Without the constituency change, procedures would
not have changed and without the change in procedures, party polarization would be nothing
more than a miniscule increasing trend.
         As Jones (1968) make clear, these conditional party government (Aldrich and Rohde
(2001) or party cartel (Cox and McCubbins Forthcoming) explanations only accounts for half
of the story of member voting. While party is powerful on procedures, constituencies are
powerful on substance. At the final stage, leaders are worried that forcing their fellow
partisans to cast party loyal votes may cause trouble for them in their constituencies. For
example, Representative Silvio Conte, the ranking Republican member on the Appropriations
Committee in the 1980s, famously remarked that his party would frequently tell him on
which votes he should shun the party to maintain electoral viability in his liberal
Massachusetts district (Edwards 2005). Froman and Ripley (1965, 61) find that this “Conte
effect” is pervasive: “For some members, on some issues, voting against the party leadership
is perceived as a necessary step to re-election.” Miller and Stokes (1963), Arnold (1990),
and Theriault (2005) show through difference explanations how constituencies affect
members’ substantive voting.

Party Polarization in Congress                                     13

Testing the Uniqueness of Procedural Votes
        If, as the second explanation argues, procedural votes are simply precursors to final
outcome votes, they should be subject to the same sorts of pressures as final passage votes.
The third explanation, on the other hand, argues that procedural votes are different from
substantive votes and that that difference gives rise to members facing a different set of
pressures when casting these different kinds of votes. I flesh out this debate with two tests.
Before presenting the tests, I describe the data that will be used to perform the tests.
        The party disparity scores cannot provide an adequate test for these explanations.
Those macro data need to be transformed into micro – individual – level data to measure
appropriately the influences that members face in casting these different votes. The
dependent variables for both tests measure procedural and substantive Republican party
support scores for each representative and senator in each Congress.13 The Republican party
support scores are composed of votes where a majority from one party votes against a
majority from the other party. After paring down the original 2,672 votes (7,028 total votes
minus the 4,356 amendment votes) to those where majorities from both parties disagreed, the
analysis is conducted on 614 procedural and 313 substantive roll call votes in the House and
478 procedural and 141 substantive roll call votes in the Senate from the 93rd Congress
through the 108th Congress (1973-2004).
        The first test measures how similar members’ procedural voting is to their substantive
voting. If the second argument is correct, the divisiveness in substance backs up into the
procedural debate implying that the members are similarly ordered from least conservative to
most conservative. The only difference between procedural and substantive voting is the
placement of the cut point between the ayes and nays, which should result in a high
correlation between procedural and substantive voting. On the other hand, if the third
argument is correct, members should have one line-up for procedural voting, which is based
on party identification, and a second line-up for substantive voting, which is based on their
constituencies’ partisanship. As such, the scores should only be as correlated as party
identification and the constituencies’ partisanship is correlated, which is 0.52 in the House
and 0.28 in the Senate.
        In short, the categories of votes are highly associated with one another. The
correlations between Republican party support scores on procedural and substantive votes are
0.91 in the House and 0.85 in the Senate. The correlations in both chambers though are
inflated because of the growing divide between the parties on both scores (i.e., the cut points
increasingly separate Democrats from Republicans on both types of votes). Although still
easily achieving statistical significance, the correlations across the vote types for only the
Republicans are 0.72 in the House and 0.64 in the Senate. The correlations for Democrats
are 0.70 in the House 0.45 in the Senate. The voting across vote types is highly correlated,
though not perfectly correlated. The first test tilts slightly to the second explanation that the
same underlying factors similarly influence votes on procedure and substance.
        The second test more directly evaluates the underlying causes of procedural and
substantive voting. If, as the second explanation suggests, the influences on members’ votes
on substance and procedure are similar, the regressions explaining procedural and substantive

13
  Just as the amendments acted partly like procedural votes and party like substantive votes in the
earlier analysis, so do they in the analysis that follows. To simplify the tests and the exposition, I
delete the category from the remaining analyses.

Theriault                                            14

voting should be quite similar. On the other hand, if the influences differ, the regressions
should also differ. In this more complex test, I include two key independent variables. First,
a Republican party indicator variable should have a larger impact on procedural votes than on
substantive votes if the third explanation is correct. As Froman and Ripley (1965, 58)
explain, “The influence of party can be relatively great in the absence of contrary pressures.
Most members want to support the party. It is only when party pressures run contrary to
other pressures that defections are likely to occur.” Second, the partisanship of the members’
constituencies, which is based on the districts’ normalized presidential vote totals averaged
over the decade, should have a larger impact on substantive votes than on procedural votes if
the third argument is correct. If the coefficients on partisan identification and constituencies’
partisanship do not differ across the regressions, we will have more evidence for the second
explanation. To account for all the variations over time, I interact a time trend variable with
both key independent variables.14
        The numbers of observation range from 6917 to 6938 in the House (corresponding to
6960 observations – the 435 members’ unity scores in 16 congresses – plus members elected
in special elections and minus vacancies and members with insufficient data) and 1505 to
1596 in the Senate.15 The regressions perform well. In every case, the overall R2 is above
0.68, with a multitude of statistically significant independent variables (see table 2). In the
eight regression equations corresponding to the 2 types of votes and 2 different chambers,
every variable is significant except the time trend and the time trend of the constituencies’
partisanship in the Senate.
Insert Table 2.
        Because of the interaction of the time trends, it is difficult to see whether the results
contained in table 2 support the second or the third explanation. The graphical depiction of
the regression results presented in figure 10 shows strong support for the third explanation,
but only in the most recent congresses. In the 93rd Congress, the change in partisan
identification caused a 9 percentage point larger impact on procedural votes than substantive
votes in the House. In the 108th Congress, the gap became 25 percentage points. In the 93rd
Congress, the change in the representative’s constituency’s impact on procedural votes than
substantive votes in the House was 2 percentage points, a tiny substantive difference in the
wrong direction. In the 108th Congress, the direction switched and the magnitude became
much greater (22 percentage points). The percentages in the Senate are similar.
Insert Figure 10.

14
   I add one additional specification to the model. An assumption of OLS regression is that the
observations are independent from one another. Because of the panel nature of the data (i.e., different
observation from the same member over time), each observation from a given member is dependent
upon the other observations from that member. As such, I initially included a member fixed effect in
the model’s specification. The results from the constituencies’ partisanships do not appreciably
change. The fixed effects specification prohibits the model from estimating a coefficient on
members’ partisan identifications because of its linear dependence. So that the members’ partisan
identification can be estimated, I report results from a random effects specification. The inclusion of
random effects does not appreciably change the substantive results of the more simple OLS
regression.
15
   If a member did not cast at least five votes in the forming of their support scores, the observation
was deleted from the analysis so that the relationships are not tested on unreliable data.

Party Polarization in Congress                              15

         In the 108th Congress, the results from the second test point directly to the third
explanation that procedural votes have a different underlying causal structure than
substantive votes. A switch in party identification changes almost completely the members
votes on procedural matters. A switch in their constituency, however, has almost no impact
on their procedural votes. Party continues to matter on substantive votes, though not as much
as it did on procedural votes. Additionally, party constituency has a marked distinction on
substantive votes.
         The time trends, whose endpoints are depicted in figure 10, add more credibility to
the third explanation. The largest differences between the 93rd and 108th Congresses are
growing importance of party identification on both procedural and substantive votes and the
decline of relevance of constituency on procedural voting. Just as the party leadership’s
power has grown over this time period, so has its dominance on procedural votes. The
increase in power has also spilled over on to substantive votes. The impact of the
constituency’s partisanship has been fairly constant over the 32 years, which makes sense.
Constituents today exercise the same power (and amount?) that they did 32 years ago: the
power to defeat incumbents at the ballot box.
         Given the disjoint between members’ influences on procedural votes and their
influences on substantive votes, scholars should tread carefully when making claims about
members’ substantive preferences. The combined effect of the increasing proportion of
procedural votes and the higher probability of middle-of-the-distribution cutpoints on
procedural votes results in DW-NOMINATE score’s increasing exaggeration of real
substantive polarization between the party caucuses in Congress. Snyder’s (1992) logic for
the artificial extremism of interest group ratings can be applied to the artificial extremism of
DW-NOMINATE to measure substantive preferences. In reality, the inclusion of procedural
votes in scaling techniques like DW-NOMINATE has three consequences. First, it
exaggerates the extent of substantive party polarization. Second, it underestimates the
relationship between members’ substantive preferences and their roll-call votes. Third, it
also underestimates the effect of constituency preferences on their roll-call votes.

V. Conclusion

         A misreading of this article would conclude that party polarization is not real and that
the members of the opposing parties do not vote differently on substantive matters in the
House and Senate. In fact, the findings presented in this article show that party polarization
is real and increasing and that the parties do vote differently on substantive matters and over
time have increasingly voted differently. Those simple conclusions, which are as pervasive
as any findings in the party polarization literature, represent an inaccurate – not an incorrect –
picture of party polarization in Congress over the last 30 years.
         While the parties are polarizing, they are increasingly polarizing on procedural
matters. In fact, nearly the entire growth in party polarization since the early 1970s can be
explained by the increasing frequency of and increasing polarization on procedural votes. In
both the House of Representatives and the Senate, the members are casting an increasing
proportion of their votes on deciding the manner of their debate rather than the substance of
the legislation. Because the substance is consuming a smaller share of the total votes cast
and because polarization on these substantive votes has not grown nearly as quickly as the

Theriault                                         16

polarization on procedural votes, the share of polarization caused by substance has stayed
about the same since Richard Nixon was president and Carl Albert was Speaker of the
House.
         Finding that the increase in and polarization on procedural votes explains almost the
entirety of party polarization only begs the question of what are procedural votes? This
paper offers only a preliminary answer. Through sophisticated or rational eyes, procedural
votes should be viewed as quasi-substantive. By deciding upon procedure, members are
affecting their ability to amend the legislation. Nonetheless, members increasingly act very
differently when they vote on procedure and when they vote on substance. In Carl Albert’s
day, they acted similarly on both types of votes. Over time, however, members increasingly
listen to their party on procedure and to their constituents on substance.
         By recognizing that procedural votes cause most of the increase in party polarization
and that procedural votes are increasingly distinct from substantive votes – at least in
members’ eyes – a clearer picture of party polarization emerges. This picture is more
consistent with the general thrust of the party literature in political science. Rather than
trying to make our square peg fit a round hole as political scientists have been trying to do in
relating large increases in polarization between the parties in Congress with rather minor
changes in the electorate, this study concludes that the disjoint can largely be explained by
the increasing reliance on complex and restrictive procedures in both the House and the
Senate. To that end, hopefully these comments are a prologue to a broader conversation
about what procedural votes are and how they affect debate inside Congress and democratic
accountability and responsiveness in the United States.

Party Polarization in Congress                            17

Bibliography
Abramowitz, Alan, Brad Alexander, and Matthew Gunning. 2006. “Incumbency,
       Redistricting, and the Decline of Competition in U.S. House Elections” Journal of
       Politics 68 (February): 75-88..
Aldrich, John H., and David W. Rohde. 2001. “The Logic of Conditional Party
       Government: Revisiting the Electoral Connection” in Congress Reconsidered, 7th
       Edition, eds., Lawrence C. Dodd and Bruce I. Oppenheimer. Washington, D.C.: CQ
       Press.
Aldrich, John H. 1995. Why Parties? The Origins and Transformation of Political Parties
       in America. Chicago: University of Chicago Press.
Ansolabehere, Stephen, James M. Snyder, Jr., and Charles Stewart III. 2001. “The Effects
      of Party and Preferences on Congressional Roll-Call Voting.” Legislative Studies
      Quarterly 26 (November): 533-572.
Arnold, R. Douglas. 1990. The Logic of Congressional Action. New Haven, Connecticut:
       Yale University Press.
Binder, Sarah A. 2005. “Ten More Years of Republican Rule?” Perspectives on Politics 3
       (September): 541-3.
Binder, Sarah A. 1997. Minority Rights, Majority Rule: Partisanship and the Development
       of Congress. New York: Cambridge University Press.
Bishop, Bill. May 30, 2004. “A Steady Slide Toward a More Partisan Union,” Austin
       American-Statesman, A1 and A8.
Brewer, Mark D., Mack D. Mariani, and Jeffrey M. Stonecash. 2002. “Northern Democrats
      and Party Polarization in the U.S. House.” Legislative Studies Quarterly 27 (August):
      423-444.
Carson, Jamie, Michael H. Crespin, Charles J. Finocchiaro, and David W. Rohde. 2004.
       “Linking Congressional Districts Across Time: Redistricting and Party Polarization in
       Congress.” Paper presented at the 2004 Annual Meeting of the Midwest Political
       Science Association.
Coleman, John J. 1997. “The Decline and Resurgence of Congressional Party Conflict.”
      Journal of Politics 59 (February): 165-184.
Collie, Melissa P. and John Lyman Mason. 2000. “The Electoral Connection Between Party
        and Constituency Reconsidered: Evidence from the U.S. House of Representatives,
        1972-1994” in David W. Brady, John F. Cogan, and Morris P. Fiorina (eds.)
        Continuity and Change in House Elections, pp. xx. Stanford, California: Stanford
        University Press.
Cox, Gary W., and Mathew D. McCubbins. Forthcoming. Setting the Agenda: Responsible
      Party Government in the U.S. House of Representatives.
Cox, Gary W., and Keith T. Poole. 2002. “On Measuring Partisanship in Roll-Call Voting:
      The U.S. House of Representatives, 1877-1999.” American Journal of Political
      Science 46 (July): 477-489..