voteview blog

Below we use first dimension DW-NOMINATE scores, which represent legislators’ positions along the familiar ideological (liberal-conservative) spectrum, with lower (negative) scores indicating greater liberalism, and higher (positive) scores denoting conservatism, to plot the chamber means for legislators and winning outcomes on roll calls for Congresses 46 to 112 (2011). These are updates to Figure 4.1 (page 60) in Poole and Rosenthal’s Congress: A Political-Economic History of Roll Call Voting and Figure 4.1 (page 80) of Ideology and Congress.

We see that the overall chamber means (plotted with red squares) remain mostly stable over time, a reflection of a competitive two-party system. Of the two chambers, the House mean has shifted more to the right in the period following the 104th Congress (the 1994 “Republican Revolution”). However, the position of the mean winning coordinate in each chamber has proved much more volatile– particularly in recent Congresses. This reflects the frequency of party-line votes between rival partisan coalitions that have moved steadily apart in recent decades.

Consequently, the mean winning coordinate– which is an approximation of the ideological location of policies enacted in the chamber– has diverged from the overall mean chamber score: to the left under Democratic control, to the right under Republican control. Indeed, the mean winning coordinate in the 111th Senate (a session in which the number of Senate Democrats fluctuated between 57 and a supermajority of 60) was the furthest to the left since the 75th Senate during the Great Depression and the New Deal. Further, the mean winning coordinate in the (present) 112th House is the most conservative since the late nineteenth and early twentieth centuries, following the realigning election of 1896, after which Republicans controlled the House for 32 of the next 38 years.

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Below we continue our analysis of how the first year of the 112th Congress (2011) fits into the contemporary trend of political polarization. In this post, we use Common Space DW-NOMINATE scores– a measure which permits direct comparison of the ideological (liberal-conservative) positions of members of the House and Senate across different Congresses. Because ideal points are estimated via joint scaling, Common Space scores are constant– that is, each member retains the same location throughout her congressional career (see Poole [2007]: “Changing Minds? Not in Congress!”).

Consequently, the differences in the histogram below–which compares the distribution of members of Congress along the ideological (liberal-conservative) scale in the 111th (top panel) and the 112th (bottom panel) Congresses–are from replacement stemming from the 2010 midterm elections. Note the loss of members along the right (moderate) edge of the Democratic distribution, many of whom were centrist Democrats defeated in the 2010 Republican wave. However, many of their Republican replacements in the 112th Congress have proven to be reliable conservative, adding to the peak of the Republican distribution center just to the left of 0.5. We also add the locations of (Senators) Obama and Clinton and Sen. John McCain (R-AZ) for reference. McCain is now clearly in the moderate camp of the Republican Party; while Obama and Clinton, a bit to the left of the center of the Democratic distribution in 2009-2010, are now just to the right of the median congressional Democrat in the 112th Congress.

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We also replicate the plot in our previous post that shows the difference in party means in the House and Senate over time. Using Common Space scores supports our finding that there has been a considerable uptick in polarization in the first year of the 112th Congress, continuing a trend which has continued unabated over recent decades.

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In a series of plots below, we show that polarization between the two parties in Congress has continued to increase through 2011 – the first year of the 112th Congress. Congressional polarization is measured below as the difference between the Republican and Democratic means on the first DW-NOMINATE dimension, which represents the ideological (liberal-conservative) scale. With the data from 2011, it has become increasingly clear that Congress is now more polarized than at any time since the late 19th century. Indeed, the growth in the distance between the two parties from the 111th to the 112th House was the largest since that following the Republican takeover of the House in the 1994 midterm elections (0.071 versus 0.085 in 1994):

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Next, we isolate the locations of the Republican and Democratic means over time in each chamber. Both parties have been trending away from the ideological middle in recent decades. This pattern is most pronounced for Republicans in the Senate and, especially, the House. Much of this is attributable to the Republican Party’s sharp rightward shift on economic issues: government regulation, taxes, and redistribution. In addition, the dwindling number of conservative, Southern “Blue Dog” Democrats in Congress has produced a more liberal Democratic coalition, with the impending retirements or defeats of Democratic moderates like Senators Ben Nelson (D-NE), Max Baucus (D-MT), and Bill Nelson (D-FL) likely to supplement this trend after the 2012 elections.

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Finally, we emphasize the disappearance of moderates in Congress by plotting the percentage of “overlapping” members in each chamber over time. Overlapping members are those Republicans who are to the left (more liberal) than the most conservative Democrat; and conversely, Democrats to the right of the most liberal Republican. At their peak, overlapping members comprised majorities in each chamber. In the last few Congresses, the overlap has vanished; that is, the most liberal Republican is to the right of the most conservative Democrat (in fact, this distance in the House is a sizable 0.187, in the Senate it is only 0.044 – between Senators Susan Collins (R-ME) and Ben Nelson (R-NE)).

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Below we use data from the Center for Responsive Politics on the estimated 2010 personal wealth of members of Congress and members’ first dimension (ideological) DW-NOMINATE Common Space scores to plot the relationship between ideology and personal wealth for present members of Congress.

More technically, we take the log of members’ estimated wealth, as is customary with variables like income or campaign spending because changes are more influential when values are small than when they are large. For example, accumulating an extra $50,000 has a far larger effect on a a political scientist than it would on Bill Gates. Logged scales adjust for this distortion.

In addition, we plot a lowess smoother to look for evidence of a systematic relationship between ideological position and level of personal wealth (for example, if conservative members are wealthier than liberal ones, or if extremists on both sides are wealthier than their moderate counterparts). We find no ideological patterns in the data: average wealth remains steady as we move along the liberal-conservative scale. Anecdotally, this conclusion is supported by a quick examination of the six wealthiest members of Congress in 2010, a list which spans ideological and partisan divides in the 112th Congress: Representatives Darrell Issa (R-CA) [0.538], Michael McCaul (R-TX) [0.456], Jane Harman (D-CA) [-0.289], and Nancy Pelosi (D-CA) [-0.544]; and Senators Kerb Kohl (D-WI) [-0.284] and John Kerry (D-MA) [-0.386].

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