You’re going to read two things today about the electoral implications of the death of Osama bin Laden: that this ensures Barack Obama’s reelection (sample here, or see big spike at Intrade), or that it will produce a short bump in approval ratings that will be gone long before November 2012 (see, for example, Nate Silver, Jonathan Chait and Jamelle Bouie).

This is an easy one: Silver and others who downplay the electoral significance of this event are almost certainly correct. I’ve seen several people compare the event to George H.W. Bush and the Gulf War, and that’s fair enough, but the most obvious comparison is to the Brits dumping Winston Churchill in 1945 or Americans turning against Harry Truman’s Democrats in 1946.

It’s going to be hard to run against Obama . . . for the next few weeks. Which doesn’t matter much electorally, since he won’t be on a ballot for the next few weeks. After that, the most likely result is that, assuming no other events intervene, things will return more or less to normal. We have 50 years of data on rally-round-the-flag effects, and what they tell us is that the half-life on these things isn’t very long. To be sure, I’m expecting a whopping big rally here (I’m guessing on the order of 15 points in Obama’s Gallup approval rating, but more is certainly possible; Seth Masket is guessing a bit less), but it won’t last, and it won’t have a whole lot of long-term effects.

Could it change some votes in November 2012, on the margins? Sure; I wouldn’t rule out something small. But mostly, almost anything that happens in May 2011 is going to be ancient history 18 months later. And certainly anything that has no day-to-day impact on the lives of most Americans. The death of bin Laden may change some of the ways that people talk about the president and foreign policy, but it’s not very likely to have any significant direct electoral effect. Of course, in a close enough race, any small shift at all could make all the difference.

Indirect effects are more likely. Masket and Kevin Drum both mention the possibility that potential candidates currently on the fence may choose not to run, presumably if the rally in Obama’s approval rating is large enough and lasts long enough. On the other hand, I find it hard to believe that much depends on whether Mitch Daniels is in or out. More plausible is the possibility that changes in the candidate fields for House, Senate and other elections could matter next November. Presidential elections are almost always contested by two reasonably acceptable candidates, but there are plenty of congressional races that are walkovers because no quality challenger emerged, and we know that potential candidates do consider the partisan electoral climate when making their decisions. If there’s an electoral effect of last night’s news, it’s most likely to show up in those down-ballot races.