One of the fears about the fallout from a hard-fought presidential primary season is the possibility of a “sore loser” effect, in which a substantial number of voters who supported the losing candidate vote for the nominee of the other party. This is a growing concern for Dems in ’08, particularly in light of McCain’s much-trumpeted crossover appeal.
Alan I. Abramowitz addresses the issue in his post “Will Disappointed Dems Vote for McCain? Crossover voting and defection in past elections” at Larry J. Sabato’s Crystal Ball. Abramowitz, author of Voice of the People: Elections and Voting Behavior in the United States, crunches the numbers from past elections and polls, and his tightly-argued analysis provides encouragement for Dems. As Abramowitz concludes,

This November, barring a major disaster at the Democratic convention, it is highly unlikely that many Democratic voters will cross party lines to vote for John McCain. It is equally unlikely that many Republican voters will cross party lines to vote for Barack Obama or Hillary Clinton. In contrast to the fluidity and unpredictability that has characterized the nomination contests in both parties, the voting patterns in November will be highly predictable and consistent with those seen in other recent general elections — close to 90 percent of all votes will be cast by party identifiers for their own party’s presidential candidate. Whichever party turns out more of its own supporters on Election Day is likely to emerge as the winner.

Clearly the downside for Dems here is that hopes for our nominee getting substantial Republican votes are also not well-supported by historical data. Better to put all of that hopeful energy into mobilizing and turning out Democrats and Independents.