Nate Silver has a good piece on the question of whether unemployment rate affects the chances for re-election:

Make no mistake: The higher the unemployment rate in November 2012, the less likely President Obama is to win a second term.

But we should be careful about asserting that there is any particular threshold at which Mr. Obama would go from favorite to underdog, or any magic number at which his re-election would either become impossible or a fait accompli. Historically, the relationship between the unemployment rate and a president's performance at the next election is complicated and tenuous.

An article in today's Times notes, for example, that "no American president since Franklin Delano Roosevelt has won a second term in office when the unemployment rate on Election Day topped 7.2 percent." The 7.2 percent figure refers to Ronald Reagan, who resoundingly won a second term when the unemployment rate was at that number in November 1984.

This type of data may be of limited utility for predictive purposes, however. Reagan won re-election by 18 points in 1984, suggesting that he had quite a bit of slack. An unemployment rate of 7.5 percent would presumably have been good enough to win him another term, as might have one of 8.0 percent, 8.5 percent or even higher.

It's also a fact that when Reagan was elected in 1980, the rate was 7.5%, although on its way up to 10%. It's got more to do with perception than raw numbers, which means that President Obama might squeak through for another term if the current rate of unemployment is going down at a reasonably fast rate in November of 2012.

Silver concludes: "[H]istorically, the correlation between the unemployment rate and a president's performance at the next election has been essentially zero." That should prevent some complacency on the GOP side going into the campaign.