Simulating the Syria Resolution Vote in the Full Senate

Yesterday, the Senate Foreign Relations Committee voted 10-7 to approve President Obama’s request to conduct military strikes against Syria (one member of the committee–Ed Markey–courageously voted “present”).
With the Syrian resolution clearing the committee stage, it now heads to the full Senate. But the question is: Will the full Senate pass the resolution?  We will get an answer next week.  But in the mean time, I took a stab at this question by simulating the full chamber vote (spoiler alert, the estimated vote is 56 for – 44 against).

Now, there are some strong caveats that accompany this post.  Namely, this is a difficult question to answer with any certainty.  First, the committee vote didn’t fall along clearly identifiable lines.  For starters, the vote (somewhat) split the parties.  Two Democrats voted against the resolution (Tom Udall and Chris Murphy) while three Republicans supported it (Bob Corker, Jeff Flake, and John McCain).  Relatedly, the vote crossed ideological lines as well (but as with party, only “somewhat”).  What seemed to matter most are state demographics, reelection, and tenure.  For example, if we eyeball the data, the state normal vote–capturing how Obama performed in 2012–seems to have had a meaningful effect.  Perhaps most notably, Tom Udall is up for reelection and represents a state Obama narrowly won.  I’m positing that both factors are key to explaining yesterday’s vote.  Finally, the length of service in the Senate appears relevant.  Looking at the data, the average number of terms served by those opposed to the resolution is 1.3 while the average terms served by those in favor of the resolution is 4.5.

Nonetheless, the patterns are difficult to eyeball, hence a multivariate analysis is needed (see also Ed O’Keefe’s post at the Washington Post) .  Details on the methods are at the bottom.  Logit results in the table the below (1=vote for the resolution, 0=vote against).

While it’s a little surprising to see most coefficients turn up statistically significant given the limited sample size, each one is in an intuitive direction.  (note: thanks to Brendan Nyhan for pointing out the issues with two clusters.  As he notes, however, this has no effect on the predicted probabilities).

The most substantively important factor is the interaction between the state normal vote and reelection.  The model predicts that a handful of vulnerable Democrats will oppose the resolution in the full Senate.  Indeed, and as Joshua Tucker argues, while national public opinion is unlikely to affect the decision to attack Syria, public sentiment may matter at the state- or district-level.  As an aside, this dynamic may explain whether (when?) the resolution fails in the House.  While the ideological and partisan dynamics of the vote are somewhat tenuous, House Republicans in conservative districts can be expected to vote no–in part–because they’re all running for reelection (unlike in the Senate, what with its staggered terms an all).  Fancy modeling aside, there appears to be tenuous support for the resolution–at best–among Republicans in the lower chamber.

But second, the number of terms served in the Senate seems to have had a substantively meaningful effect on the vote as well.  This could represent a number of things (most likely seems to be an establishment vs. outsider effect).  Thirdly, party mattered somewhat, with Democrats more likely to vote for the resolution than Republicans (once we control for other factors).  This is unsurprising.

Finally, and perhaps most importantly, I used the above model to simulate the vote in the full chamber.  Based on a senator’s predicted probability (table below, right column), I estimate that the resolution would pass 56-44.  While this is a simple majority, it is not a filibuster proof supermajority.  It’s unclear whether conservatives will filibuster the resolution.  However, Rand Paul walked back this possibility during yesterday’s markup.

Interestingly, the predicted probabilities show a number of Republicans joining Democrats and vice versa.  For example, the model predicts that Democrats Mark Pryor and and Mark Begich will vote “no” in the full chamber while Republicans Chuck Grassley and Orrin Hatch will vote “yes.”  Indeed, both Pryor and Begich are up for reelection in “red states.” In sum, the model predicts that 17 Republicans and 39 Democrats will vote for the resolution while 29 Republicans will join 15 Democrats in opposition.

Here’s the predicted probabilities.  The data are sorted based on a senator’s estimated probability of voting for the resolution in the full chamber (lowest at the top).