Below we use DW-NOMINATE scores updated through the August recess of the 113th Congress to plot the mean first dimension (liberal-conservative) scores of Republicans and Democrats and the difference in these party means over time. We previously looked at the House, and in this post we examine over-time polarization in the Senate. Using the difference of party means as a measure of polarization, we find that polarization also increased from 0.86 in the 112th Senate to 0.91 in the 113th Senate.
Like the House, the Senate continues to set new record levels of polarization dating back to the late nineteenth/early twentieth centuries. Both Democrats and Republicans moved further away from the ideological center in the 113th Senate, as the mean Democrat moved from -0.36 to -0.39 and the mean Republican moved from 0.50 to 0.53 between the 112th and 113th Senate.