To the best of my knowledge, no prominent peer-reviewed article in political science has reported a difference in the frequency with which the United States enters into conflict under Democratic presidents relative to Republican presidents.  That’s not because no one has looked for such a difference (I know I have).  It’s because, to date, no one has found one.  This is the file drawer problem in action.

Now, we want to be careful not to over-interpret that.  Absence of evidence is not evidence of absence.  There could be lots of reasons why we might fail to observe such a difference even if it was true that one party was significantly more hawkish than the other.  But when we look at other democracies, we DO find clear evidence that left-leaning governments involve their nations in conflict less often than do right-leaning governments.

As we head into the third presidential debate, it’s worth keeping this in mind.  I am reluctant to say that there’s  not much difference between what US foreign policy would look like under a second Obama administration and what it would look like under a Romney administration.  I can’t know that for a certainty.  But the past provides relatively little clear evidence that those who believe it will can point to.

But wait, you say.  What about Bush?  How can I believe that a Gore administration would have taken the US to war in Iraq?

Well, for starters, Clinton may have selected Gore to be his running mate in 1992 in part because he voted to authorize the Gulf War whereas most prominent Democrats had not.  In the closing days of the 1992 campaign, Gore essentially accused Bush of appeasing Saddam, suggesting that there’d have been no need for war if Bush hadn’t tried so hard to befriend him.  Soft on Iraq, Al Gore was not.  Or you might consider all the statements made by Democrats in the late nineties up through 2002 about Iraq and WMD (seriously, go click on that link), or the international town hall meeting the Clinton administration held in February of 1998 to communicate the administration’s dedication to destroying Iraq’s stockpile of WMD, or the bill passed with bipartisan support in the same year calling for regime change.  And, again, there’s the fact that the US has not involved itself in conflict more often under Republicans than Democrats since 1945.  But if you’re still convinced that the 2000 presidential election proved to be very consequential for foreign policy — and I’m willing to entertain such arguments, even if I’m less willing than most to accept them on face value — that doesn’t tell us whether the same will hold in 2012.

There are two important points here.  First, what candidates say they will do in terms of foreign policy is not exactly a perfect predictor of what they’ll actually do in office, any more than opposition to policies enacted by someone else after the fact proves that one would not have pursued the same policy.  Note that Obama’s primary victory over Clinton may well have been driven by the perception of him as an anti-war candidate.  Granted, those who were surprised when he escalated US involvement in Afghanistan clearly didn’t pay close enough attention to what he actually said on the campaign trail.  But neither did he position himself as the type of person who would conduct more drone strikes than Bush (by a considerable margin), nor was it clear that Obama would keep Gitmo open, declare it legal to kill US citizens without first trying and convicting them of crimes, and so forth.

Second, note that Romney’s foreign policy platform to date can be summarized as “I’ll do what Obama would do, but I’ll do it with more swagger.”  Even setting aside concerns about how well campaign rhetoric predicts policy choices made in office (has anyone looked at this systematically?), there’s relatively little difference between the policies these two candidates are currently telling us that they would pursue.

There may not even be much of a puzzle here.  Studies that have found systematic differences in the frequency with which democratic states enter into conflict under left-leaning governments relative to right-leaning governments, such as the one I linked to above, largely focus on minor powers who are allied with the US.  In such countries, foreign policy is largely a luxury good.  By that, I mean that these states look to the US to address their greatest security threats.  A left-leaning government in such a state can refrain from responding to minor incidents in a hostile manner without much affecting their security.  Similarly, a right-leaning government can behave a bit more aggressively when dealing with minor incidents, content in the knowledge that their actions will have little impact on the nation’s security.  Put differently, when you outsource large part of your security policy to a superpower, you can afford to treat the areas you retain control over as a venue for symbolic politics.  The smaller you are, the more you can afford to cater to your base without compromising your security.  Superpowers might be playing by different rules though.

Again, to be clear, I’m not saying that we know for a certainty that there’s no difference between US foreign policy under Democratic and Republican presidents.  What I’m saying is that we have some theoretical reason to expect that there might not be much difference, and an absence of persuasive evidence that there is much of a difference.  There’s always the possibility that existing attempts to establish a difference between the parties have overlooked something important, or that this time will be different.  And I haven’t said a word about the impact of the party of the president on domestic policy (nor shall I, since that’s a subject that’s well outside my area of expertise).  But it’s at least plausible that the difference between how Democratic and Republican presidents behave in office, with respect to foreign policy, is far smaller than many realize.