The Obama-Clinton wars — how much fall out?

Will the bitter contest between Barack Obama and Hillary Clinton cause many Democratic supporters of the eventual loser to defect to John McCain in November? This poll suggests that it will, at least in the must-win (for Democrats) state of Pennsylvania. The poll, taken by Franklin & Marshall College, reports that 20 percent of registered Democrats in that state who support Obama say they will vote for McCain if Clinton obtains the nomination. Similarly, 19 percent of Clinton supporters claim they will defect if Obama is the nominee.
For what it’s worth, I don’t believe the defection rate will be anything close to 20 percent in any state regardless of who the Dems nominate. Passions are running high right now, but there’s very little substantive difference between Clinton and Obama and, when things cool down, Democratic voters probably will realize this. I suspect that the Democratic defection rate if Obama is nominated (as now seems likely) will be quite low. If Clinton snares the nomination the defection rate will be a bit higher, but will consist mostly of Obama supporters who simply stay home.
The real concern for Democrats should be with independent voters. The problem here is not so much the bitter primary contests, but the fact that McCain is, well, far more independent than Clinton and Obama. Indeed, the real significance (if any) of all those Pennsylvania Dems who say they’ll vote for McCain is not that they are actually likely to vote for him, but rather that they regard McCain highly enough to contemplate doing so. For similar reasons, Independents regard McCain highly enough to vote for him, in droves.