Still, what about the apparent excess of Bush voters in 2006? Steve Freeman and others have pointed to a similar phenomenon in 2004. In 2004, the weighted national exit poll tabulation indicates that 43 percent of voters had voted for Bush in 2000 and only 37 percent had voted for Gore. It is not even possible for 43 percent of the 2004 electorate to have voted for Bush in 2000. Freeman argues that the exit pollsters entered what he facetiously calls a "Wonderland of numbers," in effect inventing millions of Bush 2000 voters to provide Bush's winning margin in 2004. However, the argument assumes that exit poll respondents correctly report their past presidential votes. Do they?

Well, no. The evidence indicates that exit polls (and other surveys) tend to exaggerate the previous winner's vote share. Of the twenty presidential exit polls archived in the Inter-university Consortium for Political and Social Research (ICPSR) collection, eighteen give the previous winner a larger margin than in the vote count. These results are displayed in Figure 1. The average change was a 7.7 percent increase in margin at the midterm, and a 11.0 percent increase in margin at the next election. These changes are influenced by differences in turnout, but the trend probably owes to outright misreporting of past votes. The change varies substantially from year to year, for reasons that are not entirely clear. Incumbent presidents with high job approval ratings tend to do better; among the losers, former presidents tend to do better than less familiar candidates. Even relatively unpopular incumbents generally do better in retrospect: It appears that some voters simply forget having voted for the loser. (I discuss this phenomenon more thoroughly elsewhere, although that 2005 analysis does not include the midterm exit poll results.)

Only twice did the incumbent's retrospective winning margin fall below the margin in the official returns. In 1994, self-described Bill Clinton voters outnumbered George H. W. Bush voters by 5.3 percent, about 0.3 points less than the official 1992 margin. And in the 1982 ABC exit poll, Ronald Reagan voters outnumbered Jimmy Carter voters by 5.8 percent, about 3.9 points less than the official 1980 margin. Note that in both cases, the losing candidate was an incumbent.

The 1982 case poses a further riddle: Reagan did worse retrospectively in the ABC exit poll, but ten points better in the CBS poll. Why the difference? Two possibilities appear. One is question order. In the ABC survey, the previous-vote question comes after a slew of questions evaluating Reagan's job performance and other political issues. These questions may have primed respondents to consider their current views of Reagan—or simply to think more about presidential politics in general—when they answered. In the CBS survey, the previous-vote question comes near the beginning. The second possible reason is that in the ABC survey, Reagan's name comes after Carter's; in the CBS survey, Reagan's name comes first! Compare 1984: Neither survey had many evaluation questions, Carter's name came first on both surveys, and the results were similar.

In short, the past-vote question is anything but "an intrinsic and objective yardstick"—and the 2006 surfeit of self-reported Bush voters is hardly surprising.