Acute partisan conflict arising from the ideological polarization of the national parties is now a dominant feature of American politics. The series of prominent showdowns over fiscal policy between Democratic president Barack Obama and the congressional Republicans that has followed the Republican takeover of the House in 2011 represent the tip of the iceberg. Partisan disputes over matters large and small, personnel as well as policy, occur almost daily. Polarized parties, combined with divided government, have made legislative gridlock the normal state of affairs in Washington, overcome only when dire necessity compels short-term compromises to stave off such disasters as default on the national debt or a government shutdown.
Conflict and gridlock have damaged the public standing of everyone involved, for most Americans detest the partisan posturing, bickering, and stalemate that leave disputes unresolved and major problems unaddressed (Hibbing and Theiss-Morse 1995). Congress's popular ratings have reached all time lows, with an average of 80% of respondents disapproving of its performance in polls taken over the past two years; barely half of Americans approve of even their own party's members and leaders. (1) Barack Obama's ratings sag with every showdown, and he has become the most polarizing president on record. (2) In polls taken since 2011, an average of more than three-quarters of respondents said they were dissatisfied with the nation's direction; dissatisfaction reached a record 88% during the summer of that year when House Republicans tried to force massive spending cuts by refusing to raise the nation's debt ceiling, thereby threatening global economic turmoil, before finally backing down. (3) "Ridiculous," "disgusting," and "stupid" topped the list of one-word descriptions of the goings-on collected by the July 28-31, 2011, Pew survey. (4) Such reactions have done little, however, to curb Republican enthusiasm for games of chicken on the edge of the fiscal cliff.
America's governing institutions are inherently prone to stalemate and, according to James Madison's famous account in Federalist 10, designedly so. The bicameral legislature, presidential veto, and separate electoral bases and calendars of representatives, senators, and presidents were intended to thwart simple majority rule, and they always have. The Senate's requirement of a supermajority of 60 votes to overcome filibusters on most types of legislation imposes yet another barrier to action. Thus when the parties are deeply divided and neither enjoys full control of the levers of government, acrimonious stalemate or unsatisfactory short-term fixes to avoid pending disaster become the order of the day.
To consider what, if anything, might alter this state of affairs, it is useful to have a clear idea of how it came to be. My purpose here is to provide a variety of summary data documenting what has happened and why. The evidence, in my view, shows that elite polarization is firmly rooted in electoral politics and is therefore likely to remain until electoral configurations somehow change. To begin, I review some well-known data confirming that the current partisan and ideological polarization of the Congress is the extension of a long-term trend. I then review the electoral underpinnings of this trend, reviewing the evolution of individual and aggregate voting patterns and showing how their interaction with the electoral system has contributed to divided government and partisan intransigence. Finally, I consider various scenarios for electoral shifts that might reduce partisan conflict and break the stalemate.
Partisan Polarization in Congress
The systematic evidence documenting the increasing partisan polarization in Congress is familiar to all congressional scholars. Keith Poole and Howard Rosenthal (joined later by Nolan McCarty) have been tracing this trend since the early 1980s through their analysis of members' first-dimension DW-Nominate scores, which are based on all nonunanimous roll call votes taken during each Congress and serve to locate each member for each Congress on a liberal-conservative scale that ranges from -1.0 to 1.0; the higher the score, the more conservative the member. (5) Figure 1 displays the trends in the average scores for Republicans and Democrats in the House and Senate since the Ninety-third Congress (1973-74), when ideological divisions between the parties were at an unusually narrow point.
Two things stand out. First, of course, is that the congressional parties have moved apart; the ideological gap has widened from .568 to .845 in the Senate, and from .527 to 1.070 in the House over this period. The gaps for both chambers the 112th Congress (2011-12) are the widest ever observed in data going back to 1879. Second, Republicans have been responsible for most of the change (more than 80% for both chambers). That is, the growing ideological distance between the parties is primarily a consequence of Republicans becoming more conservative, not Democrats becoming more liberal. This is also evident from Figures 2a, 2b, 3a, and 3b, which display the distributions of the ideological locations of Democrats and Republicans in the two Congresses bracketing this period. Both comparisons show the disappearance of the moderate centrists and the increasing ideological homogeneity of the congressional parties. Figure 4, which shows the percent of nonunanimous votes cast for the president's position on roll call votes since the Ninety-third Congress, also reveals growing partisan gap in both chambers in votes on the president's legislative agenda over the past 40 years. The current partisan divisions in Washington are not peculiar to the Obama years, but rather represent the latest extension of a decades-long trend.
Polarization's Links to Electoral Politics
The congressional parties have been driven apart by a diverse array of interacting internal and external forces, (6) but one essential factor has been the corresponding polarization of the congressional parties' respective electoral bases, which was itself in part a reaction to polarized national politics (Jacobson 2000a). Two major trends have given the congressional parties increasingly divergent electoral coalitions. First, the partisan, ideological, and policy opinions of American voters have grown more internally consistent, more distinctive between parties, and more predictive of voting in national elections (Jacobson 2000b). Second, electoral units into which voters are sorted have become more homogeneously partisan. (7) That is, over the last several decades, changes in the preferences, behavior, and distribution of congressional voters have given the congressional parties more internally homogenous, divergent and polarized electoral bases.
The main source of this electoral transformation was the partisan realignment of the South. (8) The civil rights revolution, and particularly the Voting Rights Act of 1965, brought southern blacks into southern electorates as Democrats, while moving conservative whites to abandon their ancestral allegiance to the Democratic party in favor of the ideologically and racially more compatible Republicans. In-migration also contributed to an increasingly Republican electorate, which gradually replaced conservative Democrats with conservative Republicans in southern House and Senate seats. Conservatives whites outside the South also moved toward the Republican Parry, while liberals become overwhelmingly Democratic. The level of consistency between party identification and ideology thus grew across the board. According to American National Election Study (ANES) data, in 1972, self-identified liberals and conservatives identified with the "appropriate" party 71% of the time; in 2012, they did so 84% of the time. (9) In the 2012 Cooperative Congressional Election Study (CCES), that figure exceeded 90%. (10)
Party loyalty among congressional voters also increased over this period (Jacobson 2013a, 128), so the relationship between ideology and voting became much stronger. Figure 5 displays the growing proportion of self-identified liberals and diminishing proportion of self-identified conservatives voting for Democratic candidates for House and Senate in elections since 1972. The shift among conservatives is particularly notable. In 2012, according to the ANES, 89% of self-identified liberals voted for Democrats in the House elections, while 85 % of conservatives voted for Republicans (11); in the national exit poll, the respective figures were 86%...