Last week I did a post pushing back against the security-blanket assumption of many Republicans that the general election will be a straight-forward “referendum” on the president’s policies and performance, making the palpable weaknesses of the GOP and its nominee largely irrelevant. Conservative blogger “Karl” at Ponterico’s Pontifications (in a post widely circulated among his peers) fired back with a response that mostly touted the alleged consensus of political scientists, based on relatively recent re-election campaigns, that such campaigns are indeed mainly about the incumbent. Karl also cited a 2011 piece by a colleague and mentor of mine, Bill Galston of Brookings, that reached the same conclusion; as it happens, Galston was about to publish a cautionary column at TNR warning over-confident Democrats that attacks on the GOP and Romney were unlikely to offset swing-voter concerns about Obama’s record, if they don’t improve or take a turn for the worse.

For the record, I don’t dispute that an incumbent’s record is the single most important factor in a re-election campaign, for all the obvious reasons. And if that record is bad enough or unpopular enough, it may blot out the sun. But short of that circumstance (and it’s hardly today’s situation), other factors matter, too, including swing-voter (and to some extent base-voter) perceptions of the opposing candidate and his party.

Most of the poli sci “consensus” you hear on this subject is suggestive rather than dispositive, and simply concludes that approval rating assesssments of incumbent presidents, and general perceptions of objective conditions of life (particularly the economy) have been useful predictors of past presidential re-election bids.

But if you review the literature, there are all sorts of disclaimers that have to be thrown in. For example, as Larry Bartels notes, the tendency of the incumbent party to be held responsible for conditions in the country–i.e., the extent to which an election is truly a referendum–may vary according to how long it has been in power. This matters in 2012 because memories of the Bush administration and the financial collapse of 2008 remain strong. Moreover, as Ramesh Ponnuru has argued, recent partisan polarization has reduced the weight of swing voters whose tendency to view the election as a “referendum” has accordingly lost weight as well, which is why the 2004 Bush-Kerry campaign didn’t exactly follow the “referendum” model.

But perhaps the most important reason to question the scientific certainty of the “referendum” hypothesis is that, as Nate Silver points out today, the “sample” of equivalent prior elections is limited. If the economy struggles or sours between now and November, there are just two recent presidents whose re-election campaigns provide relevant data: Carter in 1980 and Bush in 1992. A lot of things other than judgements of the incumbent were going on in both those elections, including significant third-party candidacies. And in both those elections (as in 2004, when both the president’s approval ratings were pretty similar to what we are likely to see this November), it seems clear that questions about the challenger had to be resolved before the election turned on judgements of the incumbent.

This last point is one I emphasized in my own TNR column commenting on Galston’s, and in my original post on the subject: perceptions of candidates are inherently interactive. How you feel about the incumbent or even about the status quo depends in part on how you view the alternatives. Carter’s standing sank when Reagan crossed some invisible but very real credibility threshold. George W. Bush’s approval ratings climbed after his allies spent an effective month or two bashing John Kerry, and Bush defied the “incumbent rule”–a political science dictum closely associated with the belief that re-election campaigns are referenda–that undecided voters late in a campaign will break heavily against the incumbent.

The bottom line is that “choices’ cannot be wished away from a re-election campaign by Republicans with reason to worry about perceptions of their party and its candidate, any more than Democrats can wish away perceptions of Obama’s performance. And anyone who tells you history has foreordained the result is building a house on thin and shifting sand.

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Ed Kilgore is a political columnist for New York and managing editor at the Democratic Strategist website. He was a contributing writer at the Washington Monthly from January 2012 until November 2015, and was the principal contributor to the Political Animal blog.