A number of people have requested that we provide “regular” DW-NOMINATE scores for the House and Senate using the dynamic two-dimensional model through calendar 2015. We have computed these and will post them on our data for friends page this weekend.
Below we show the polarization series for the House and Senate separate scalings. This graph is almost identical to the one in our post a few weeks ago using the Weekly CS DW-NOMINATE scores. As we noted in that post, the impact of the last three elections — 2010, 2012, and 2014 — on the Republican Party seems to have been the large influx of “Ted Cruz” Republicans. Polarization has jumped sharply from the first two years of President Obama’s first term. Polarization in the House may have leveled off (see below) but the Senate increase is much larger than the House.
The figures below show the means of the two parties in each Chamber on both dimensions over time. The House Republicans actually moderated very slightly in the first session of the 114th while the House Democrats show absolutely no difference between North and South and the two have converged. The slight uptick in polarization in the House is due to the leftward movement of the Democrats being slightly greater than the leftward movement of the Republicans.
The Senate for the most part tracks the House on the first dimension. The main difference is that there are still three Senators from the South (the eleven states of the Confederacy plus Kentucky and Oklahoma [CQ’s definition]). Those three [Nelson (D-FL), Kaine (D-VA), and Warner (D-VA)] are more moderate than their Northern counterparts. Nonetheless, the Senate Democrats are moving to the left and the Senate Republicans are moving to the right thereby increasing polarization in the Senate at a faster rate than in the House.
The Second Dimension at one time picked up conflict over Civil Rights for African Americans but, beginning in the early 1970s until the early 2000s “Social Issues” such as abortion and gun control (see Poole and Rosenthal, 1997; McCarty, Poole, and Rosenthal, February 2016). The Second Dimension has faded to insignificance but could make a come back with a possible split in the Republican Party during the 2016 elections.