El índice de aprobación de un Presidente y su techo electoral

RealClearPolitics:

One of the more fashionable debates today is whether the 2012 election will be more of a choice between two candidates, or a referendum on the party in power. Over at The New Republic, Ed Kilgore provides one of the more cogent arguments for the former.

Kilgore's assertion flies in the face of the conventional wisdom: That in an incumbent election, the electorate engages in a two-step process. First, it decides whether it likes the incumbent. If it does, the incumbent is re-elected. If it doesn’t, it then asks whether the challenger is acceptable. If the challenger is acceptable, the unpopular incumbent is defeated; if not, the incumbent is re-elected.

In other words, analysts who accept this model implicitly assume that the election is largely a referendum on the incumbent; how strong a referendum it is depends on how high you believe the bar to be cleared in Step 2 is.

(...) Let’s start with the two major examples that Kilgore advances in support of his claim: The 1980 and 2004 elections. Both of these examples actually suggest the exact opposite of what he claims. In 1980, a majority of the electorate believed that Jimmy Carter was doing a poor job, and he lost. In 2004, a majority of the electorate believed that George W. Bush was doing a good job, and he won.

Kilgore argues that the 1980 election didn’t have to turn out the way it did, and he observes, correctly, that late-breaking votes overwhelmingly chose the challenger over the incumbent president. This is widely attributed to Ronald Reagan’s outstanding debate performance in the closing weeks of the contest.

But Carter’s final job approval poll in 1980 -- unfortunately, taken in September -- shows him receiving a 37 percent approval rating, roughly similar to the 41 percent of the vote he ultimately received. Put differently, the undecided voters had to go somewhere, and one could argue that they were likely to break heavily toward Reagan, strong debate performance or not.

The other election that Kilgore discusses is similarly misunderstood. The election of 2004 is frequently held up as an example of an unpopular president winning re-election by making his opponent unacceptable to the electorate. And, indeed, Bush’s approval rating in Gallup’s final poll of the electorate was a tepid 48 percent, suggesting that he over-performed his approval rating by a decent margin.

But Gallup was an outlier that year. The final RCP Average had Dubya at 49.8 percent approval, very close to the 50.7 percent of the vote he eventually received. If one looks at the actual electorate, as measured by the exit polls, 53 percent approved of the job that Bush was doing.

This suggests that, for all the swift-boating and flip-flopping charges and whatnot, what that election really came down to was that Bush was running in an electorate that generally thought he was doing a good job. Again, one can argue that Bush's approval was boosted by bashing Kerry, but I'm not certain what real evidence we have one way or the other of this. And the bottom line remains that, whatever the reason, Bush's job approval within the electorate was above 50 percent on Election Day.

(...) The closer we look at the data, the more we see this tendency spring up. As Jay Cost has helpfully noted, in 2004 this tendency filtered down to the states as well. Bush didn’t win any states where he had a net-negative job approval, and lost a handful where he had a slightly net-positive job approval. Similarly, Cost demonstrates that, according to the National Election Study, incumbents going back to 1972 have rarely received a substantial percentage of the vote from those who disapproved of the job they were doing. This suggests that, at the very least, the bar in "Step 2" is so low that it is irrelevant in most elections.