There is a small but reasonably persistent gap between President Obama’s net approval ratings and his head-to-head polls against Mitt Romney. Whereas Mr. Obama’s approval ratings have been almost exactly breaking even for most of the past few months — in fact, they’re very slightly underwater now according to the Real Clear Politics average — he has more often than not enjoyed a slight lead in head-to-head polls against Mr. Romney.
Liberals and conservatives tend to interpret this evidence in different ways. For liberals, it may be taken as a sign that Mr. Romney is an especially weak candidate — enough so that many voters who are on the fence about Mr. Obama’s job performance, and even a few who disapprove of it, will be willing to vote for Mr. Obama if Mr. Romney is the alternative. The claim has often been made in recent weeks, for instance (in my view, based on relatively speculative evidence), that Mr. Obama’s attacks on Mr. Romney’s tenure at Bain Capital may have damaged Mr. Romney.
Conservatives instead sometimes argue that this is a sign that Mr. Obama has some softness in his numbers. As voters become more engaged with the campaign, Mr. Romney may have a bit of wind at his back if he is able to keep the focus on Mr. Obama’s job performance; the head-to-head polls could fall more in line with Mr. Obama’s approval ratings.
Neither of these views is irrational. In support of the liberal position, my research suggests that there can be some predictable-seeming differences between a president’s net approval rating and the result he actually realizes on Election Day, based in part on “candidate quality” factors related to his opponent. For instance, opponents who have especially “extreme” ideologies (who are perceived as being very liberal or very conservative) may allow a president to over-perform his approval ratings, while challengers who are viewed as moderates may get the benefit of the doubt from voters. Elections are perhaps mostly a referendum on the incumbent, but they are not purely so.