Evidence of Assymetric Polarization in Congress with Common Space Scores

There is little question that the parties in Congress have moved ideologically further apart over recent decades. But has polarization been symmetric (with both parties moving away from the center at roughly equal rates), or has it been assymetric (driven more by Republican than Democratic movement)? DW-NOMINATE scores unambigously support the claim of asymmetric polarization, but some alternate ideological measures suggest that polarization has been more symmetric.

Below we use Common Space DW-NOMINATE scores to demonstrate that the finding of asymmetric polarization is not an artifact of the time trend allowed in regular DW-NOMINATE scores. With Common Space scores, a single score is estimated for each member based on their entire (often decades-long) congressional roll call voting record. Separate scores are not estimated for each member in each Congress. Hence, the only factor that could be driving polarization in the graphs below is member replacement (for instance, when a more conservative/liberal Senator replaces a more moderate Republican/Democrat).

The 10%/90% ranges refer to the 10th and 90th ideological percentiles of Democrats and Republicans in both chambers. That is, 80% of Democrats and Republicans in the corresponding chamber fall within these bands. We see the same polarizing trends as when using standard DW-NOMINATE scores: the House has polarized more than the Senate, and Republicans have moved further away from the center than Democrats. The final graph below shows a histogram of the House and Senate distributions in the current 113th Congress, with the positions of some key past and present figures denoted. There is a clear hump on the right that is comprised of mostly new members of Congress like Senators Ted Cruz (R-TX) and Rand Paul (R-KY).

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The Senate Vote to Invoke Cloture on the Campaign Finance Amendment and the House Vote to Condemn the Taliban Prisoner Swap

Below we use Optimal Classification (OC) in R to plot the Senate’s 79-18 vote to end debate on a constitutional amendment to protect campaign finance regulations and the House’s 249-163 vote on a resolution condemning the Obama administration for not notifying Congress about the deal to exchange Taliban prisoners for Sgt. Bergdahl last June.

As seen below, the Senate vote splits Republicans and the House vote splits Democrats, both along ideological lines. The group of 18 Republicans who opposed cloture included conservative Senators like Ted Cruz (R-TX) and Rand Paul (R-TX), while the 22 House Democrats who supported the prisoner swap resolution included Blue Dogs like Reps. John Barrow (D-GA) and Jim Matheson (D-UT) as well as Senate hopefuls Reps. Bruce Braley (D-IA) and Gary Peters (D-MI). Both Braley and Peters are classification errors: on the basis of their ideological positions, the model incorrectly predicts them as Nay votes.

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House: Two Immigration Votes

Below we use Optimal Classification (OC) in R to plot the House’s two recent votes on immigration: its 223-189 vote on a$694 million appropriations bill to enact new security measures along the U.S.-Mexico border and its 216-192 vote to end the Deferred Actions for Childhood Arrivals (DACA) program. Both votes were party-line, with the exception of four Republicans and one Democrat on the border funding bill and 11 Republicans and 4 Democrats on the bill to end DACA.

Particularly on the bill to prohibit the president’s use of DACA to stop deportations, ideology appears to do a good job of capturing the handful of party crossovers. The four Yea Democrats (Reps. Barrow, McIntyre, Peterson, and Rahall) are among the most moderate House Democrats and OC correctly predicts two of these (Barrow and McIntyre) as Yea votes. The eleven Nay Republicans (Reps. Amodei, Coffman, Denham, Diaz-Balart, Gardner, Heck, Kinzinger, Reichert, Ros-Lehtinen, Valadao, and Upton) generally represent districts with larger Hispanic populations but are also in the moderate wing of the House Republican caucus.

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Note: The plots show only 222 and 215 Yea votes, respectively, because newly-elected Rep. Curt Clawson (R-FL) voted Yea on both measures but has not yet cast enough votes to be included in the scaling.

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The 50th Anniversary of the Civil Rights Act: Plotting the House and Senate Votes

Today marks the 50th anniversary of the enactment of the Civil Rights Act. The Civil Rights Act passed the House in a 290-130 vote and the Senate in a 73-27 vote. Below we use DW-NOMINATE scores to plot both votes. First dimension DW-NOMINATE scores represent legislators’ ideological positions along the liberal-conservative spectrum and, during this period (as well as throughout the mid-twentieth century), the second dimension captures regional differences among members of Congress. Regional divides were most apparent on votes involving race and civil rights issues.

Accordingly, the divide on both of these votes separating predicted “Yeas” from predicted “Nays” runs mostly along the second (regional) dimension. Most Southern Democrats (with high second dimension scores) voted against the bill in both chambers and were joined by a handful of mostly conservative Republicans (like Senator Barry Goldwater [R-AZ]). But both votes far more reflected regional differences than ideological ones.

In the half-century since passage of the Civil Rights Act, the second regional dimension has all but disappeared in congressional voting. Racial issues have become questions of redistribution (a fundamental liberal-conservative disagreement), and social/cultural issues like gun control and abortion have also folded into the liberal-conservative dimension. To illustrate this, in the final image we show how well one and two-dimensional models classify congressional voting on the issues of abortion, gay rights, gun control, and immigration. The measure of classification is the APRE (Aggregate Proportional Reduction in Error), and measures how much improvement the model offers in classification of legislators’ votes. The maximum APRE is 1 (complete improvement), while a value of 0 indicates no improvement over the null model. As can be seen, the fit of all four issues to a one-dimensional ideological (liberal-conservative) model has steadily climbed to nearly 1 over recent decades. Both racial and social/cultural issues are now largely encompassed by the primary liberal-conservative dimension.

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How Conservative is Eric Cantor?

Tonight comes the surprising news of House Majority Leader Eric Cantor’s (R-VA) primary upset by a Tea Party challenger. Just how conservative (or not) is Rep. Cantor? Using DW-NOMINATE Common Space scores (which measure the ideological positions of Members of Congress based on the entirety of their roll call voting records), we find that Cantor is more conservative than 61% of Republicans in the (current) 113th House and more conservative than 76% of Republicans in the 113th Senate.

Though already a sound conservative in the current Congress, Rep. Cantor would have been among the most conservative Republicans (more conservative than 83% of Republicans) 20 years ago in the 104th House. Below we plot the ideological distribution of Republican members of the 104th House (in light red) and of the 113th House (in dark red). We also mark the locations of the top three Republican leaders (the Speaker, Leader, and Whip) in both Congresses. Not only is Rep. Cantor the most conservative of the top three Republican leaders in the current House (Speaker John Boehner and Whip Kevin McCarthy), but is also more conservative than former Speaker Newt Gingrich.

It is also noteworthy that the current House Republican leadership is to further to the left of the rest of the party than was the case in the 104th House.

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House: Vote to Prohibit Funds for DEA Raids on State-Legalized Medical Marijuana

Below we use Optimal Classification (OC) in R to plot the House’s 219-189 vote to prohibit funds for DEA raids on medical marijuana operations in states that have legalized it.

Contrary to the narrative that it was mostly moderate Republicans who comprised the 49 GOP votes in favor of the amendment (sponsored by Rep. Dana Rohrabacher (R-CA)), the plot below shows that the Republican Yea votes are fairly even distributed along the first dimension (representing liberal-conservative position). The difference in the mean first dimension scores of House Republicans who voted Yea and Nay is negligible (0.01) and not statistically significant (p = 0.43). In part this could be because the proposal also touches on states’ rights, which may have earned it the support of even socially conservative House Republicans like Reps. Paul Broun (R-GA) and Mo Brooks (R-AL). Indeed, the second dimension appears to do a better job of dividing House Republicans than the first dimension, with libertarian-minded Republicans like Reps. Justin Amash (R-MI) and Walter Jones (R-NC) supporting the amendment and holding very high (indeed, the two highest) second dimension scores.

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House: Vote to Limit NSA Phone Surveillance

Below we use Optimal Classification (OC) in R to plot the House’s 303-121 vote to limit the National Security Agency’s controversial phone surveillance program.

As the plot below shows, there is almost no ideological organization to this vote. It would be plausible to expect that this would be a “two-ends-against-the-middle” vote; that is, that the most liberal Democrats and the most conservative Republicans would spearhead support for this measure. But, to the extent that there is an ideological pattern on this vote, it supports the opposite conclusion. The mean first dimension coordinates of Democrats voting Yea is -0.46, while the mean scores of Nay Democrats is a slightly more liberal -0.52. The most conservative House Republicans were also more likely to vote Nay, with the mean first dimension score of Yea Republicans at 0.40 and of Nay Republicans at 0.44. Of course, these differences are minor.

The cutting line (dividing predicted Yeas from predicted Nays) runs along the second dimension. But, complicating matters more, those with high second dimension scores (legislators like Rep. Justin Amash (R-MI) and Walter Jones (R-NC)) are predicted to vote Nay, even though they have been among the most vocal critics of the NSA. Many of these legislators voted Nay because the bill did not go far enough to rein in NSA surveillance programs. Because of this, it is difficult to attribute substantive meaning to the second dimension on this vote.

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Senate: Vote to Invoke Cloture on the Shaheen-Portman Energy Bill

Below we use Optimal Classification (OC) in R to plot the Senate’s failed attempt to invoke cloture on an energy efficiency bill sponsored by Senators Jeanne Shaheen (D-NH) and Rob Portman (R-OH) in a 55-36 vote. All but three Republicans (Sen. Portman along with Senators Kelly Ayotte (R-NH) and Susan Collins (R-ME)) opposed the measure to end debate because they wanted a vote on an amendment involving the Keystone XL pipeline.

Interestingly, none of the endangered Democratic Senators up for reelection in 2014—in particular, Senators Mark Begich (D-AK) and Mary Landrieu (D-LA)—voted Nay on cloture. The only Democratic Nay vote was from Senate Majority Leader Harry Reid (D-NV), but only because doing so allows him to reintroduce the measure for another vote in the near future.

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House: Vote to Hold Lois Lerner in Contempt

Below we use Optimal Classification (OC) in R to plot the House’s 231-187 vote to hold Lois Lerner in contempt of Congress. The vote was nearly party-line, with six House Democrats crossing over to vote in favor of contempt.

As the plot below shows, the six Democrats (Reps. Ron Barber (D-AZ), John Barrow (D-GA), Mike McIntyre (D-NC), Patrick Murphy (D-FL), Collin Peterson (D-MN), and Nick Rahall (D-WV)) who voted Yea are among the most centrist members of their party’s caucus. All but McIntyre are also facing tough reelection races in November, which helps explain the errors made by the spatial model. Rep. Jim Matheson (D-UT), for example, is the most moderate House Democrat, but is retiring at the end of this year and voted Nay.

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Southern Realignment through the 2012 Elections

Below we provide updated data on the southern realignment through the 2012 elections. Continuing gains among white voters has led to an increasingly Republican South (which we count as the 11 states of the Confederacy plus Kentucky and Oklahoma). In return, the image of the national Republican Party has become more closely tied to the South. As Nate Cohn notes, 41 percent of Romney voters in 2012 were from the South and a majority of House Republicans represent Southern districts.

As is well known, the Republican Party’s breakup of the Democratic Solid South occurred first at the presidential level. As seen in the first plot (showing the difference in the Republican Party presidential nominee’s vote share between the South and North), the South voted more Republican than the North starting in 1964 (Goldwater vs. Johnson) and supported Nixon more than the North against both Humphrey in 1968 and McGovern in 1972. Jimmy Carter won more support in the South than the North in both of his elections, but since 1984 the South has voted more Republican than the North in 8 consecutive presidential elections. The trend has been mostly stable since 2000: the South has voted about 10 percentage points more Republican than the North over the last four presidential elections.

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Congressional Southern Democrats have traditionally fared better than their party’s presidential nominees, but over time the congressional delegations of Southern states has become increasingly Republican. The plots below show the percentage of Southern and Northern seats in the House and Senate represented by Republicans over time. Two recent elections — 1994 and 2010 — stand out for Republican surges in the South that the Democratic Party was not able to recover in recent elections. The importance of these elections is that they used national party waves to wipe out senior conservative Southern Democrats who could not easily be replaced in later elections. Once those seats flipped Republican, they were unlikely to switch back. After 2012, more than 70% of Southern Representatives and Senators are Republicans, with most of the remaining House Democrats representing majority-minority districts.

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Finally, the last vestige of Democratic power in the South has been in the state legislatures, but steady Republican gains here have ended unified Democratic control of all Southern state legislatures (including in the last remaining state — Arkansas — in 2012). In both the upper and lower chambers, Republicans now hold more than 60% of seats in southern state legislatures.

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