With Barack Obama’s announcement yesterday that he’s creating a presidential exploratory committee, I thought it was worth comparing his voting record in the Senate with those of his rivals, especially given the hype about him being more liberal than Hillary, who has been very cautious. In particular, Obama opposed authorizing the President to use force in Iraq, while Clinton voted yes.
It turns out that UCSD political scientist Keith Poole just updated his DW-NOMINATE estimates of Congressional “ideal points,” the most widely used in the discipline, to include the 109th Congress (2005-2006), which Clinton and Obama both served in. (These estimates are created by scaling all the non-lopsided roll call votes over a series of Congresses and are therefore more reflective of a member’s overall voting record than interest group ratings, which are typically based on a handful of votes. Poole created the metric with Howard Rosenthal.)
Here’s how the distribution looks for the Senate:
As you can see, the parties are almost completely separated on ideology (the only overlap is that Nebraska Democrat Ben Nelson rates as slightly more conservative than the former Republican senator Lincoln Chafee from Rhode Island, which isn’t clear from the histograms). The Democratic mean is -.428 (closest senator: Harry Reid) and the Republican mean is .458 (closest senator: George Allen). If we look at the estimated scores and rankings for the presidential contenders, it’s striking how similar some of the Democrats are — Obama and Clinton have the exact same estimated ideal point:
Obama -.496 (tie — 14th most liberal)
Clinton -.496 (tie — 14th most liberal)
Kerry -.489 (16th most liberal)
Dodd -.447 (20th most liberal)
Biden -.324 (34th most liberal)
McCain .376 (39th most conservative)
Obama, Clinton, Kerry and Dodd are all tightly clumped in a group that is slightly more liberal than the Democratic mean, whereas Biden is (surprisingly) somewhat more conservative than the party mean. By contrast, John McCain is to the left of the Republican mean — you can see why he’s running to the right.
Still, the most striking finding is that Obama and Clinton actually have voting records that appear to be very similar in their overall liberalism.
Update 3/23 9:41 AM: As a point of comparison, the estimated ideal point for John Edwards in the 106th-108th Congresses was a somewhat more moderate -.375, while Clinton’s was stable at -.496 for the 107th-108th (Obama only entered the Senate in the 109th).
[Note: These scores are constrained to stay relatively stable across a small number of Congresses.]