The most commonly used scores for ideological distance are DW-Nominate scores, based on representatives’ actual votes. These measures reduce various flavors of “liberal” and “conservative” to a single metric, but they are the scores most widely used and trusted by political scientists and political commentators because they measure virtually all the actual votes in a careful and rigorous way. As many people have noted, there used to be lots of ideological overlap between the parties, and lots of moderates in both parties, but there is less overlap, and in particular there are fewer moderate Republicans. I decided, like some others, to look at this in light of the upcoming Senate. Beyond that, it is interesting to compare it to the Senate from 10, 20, and 30 years ago (the 108th, 103rd, and 98th Senates), so I use the DW-nominate constant scores, which provide comparable scores among the members of different Congresses. The numbers are striking, particularly on the Republican side. Just ten years ago, in the 108th Senate, there were 10 Democrats with DW-Nominate scores between −.3 and -.2 (the more negative, the more liberal), and 8 Republicans with DW-Nominate scores between .2 and .3 (the more positive, the more conservative). And there were 6 Democrats between −.2 and 0 and 7 Republicans between 0 and .2, which is probably a better reflection of what we mean by truly moderate Senators (again, with all of this measuring the distance of Senators from their colleagues past and present based on their voting records).
In the upcoming Senate, we have to do some extrapolation because we don’t have DW-Nominate scores for those who are new to the Senate (and the DW-Nominate constant scores for the House cannot simply be applied to the Senate). But Boris Shor at the University of Chicago did some calculations, about the ideologies of the Senate candidates based on their votes (where applicable) or their stated positions via VoteSmart, and as it turns out it seems pretty clear that the new Republicans in the 113th Senate are at least as conservative as the median Senate Republican in the 112th. And for my purposes, all that matters is that these new Senate Republicans will not be among the most liberal members of the Republican Senate caucus. In light of the numbers and everything we know about them, I’m willing to make that assertion about Ted Cruz, Jeff Flake, and Deb Fischer, three of the most conservative Republicans running for Senate seats this past election. The Democrats are trickier, in that there are four new Senators who will caucus with the Democrats (including Angus King) who might be among the most conservative Senate Democrats: Joe Donnelly, Heidi Heitkamp, Angus King, and Tim Kaine. In light of Donnelly’s very moderate voting record (almost perfectly the midpoint between Republicans and Democrats, according to Shor’s numbers), he in particular looks like he will be among the most conservative Democrats, but others in this group might also end up being quite moderate. To avoid making unwarranted assumptions, in the numbers below I put only one of these four, Donnelly, between −.2 and 0, and the remainder more than −.3 away from 0. If I am wrong in placing these four, that still doesn’t change the number very much. And, more importantly, it doesn’t change the really interesting and striking story — the dramatic drop in the number of moderate Republicans.
Here are the numbers for the new Senate:
Democrats between −.3 and -.2: 12
Democrats between −.2 and 0: 5
Republicans between .3 and .2: 3
Republicans between .2 and 0: 1
So here’s the change in a single chart:
Note that the National Journal’s numbers for ideology tell a similar story.
The lightest red bar is of course the most striking change. And it is remarkable that there is now just one Republican Senator with a score of .2 or less. Note that the Republicans who are third and fourth most likely to vote with the liberals (after Susan Collins at .107 and Mark Kirk at .225) are Lisa Murkowski (.241) and Thad Cochran (.292). That’s right — the voting records show that Thad Cochran is to the left of all but three Republicans in the Senate.