It may be supporters of Hillary Clinton, who still would prefer the Senator from New York as the Democratic Party’s presidential nominee. Sixty-six percent of Clinton supporters, registered Democrats who want Clinton as the nominee, are now backing Obama. That’s down from 75 percent in the end of June. Twenty-seven percent of them now say they’ll support McCain, up from 16 percent in late June.
“The number of Clinton Democrats who say they would vote for McCain has gone up 11 points since June, enough to account for most although not all of the support McCain has gained in that time,” says Holland.
. . . A majority of registered voters, 54 percent, think Obama’s choice of Delaware Senator Joe Biden as his running mate is an excellent or good decision. That number jumps to 73 percent when just asked of registered Democrats. But it drops to 59 percent when narrowed to Clinton supporters. “It's not that there's anything wrong with the choice of Joe Biden. . . . "A lot of Americans don't know who he is, but his favorable rating is 13 points higher than his unfavorables But Biden is not Hillary Clinton, and it's possible that is enough to have moved some of her supporters away from the Democratic ticket, at least temporarily."
(Emphasis supplied.) Obama did not optimize his chances for winning in November when he chose not to choose Hillary Clinton. All the whining and complaining about PUMAS is not going to help that.
Update [2008-8-24 21:19:27 by Big Tent Democrat]: While DemfromCt likes this result in the USAToday Gallup poll (Obama leads by 4 among RVs and 3 among LVs (after leading by 3 among RVs and McCain leading by 4 among LVs a month earlier), I see more support for my view that Obama did not make the best political choice for VP, only the best NOT Hillary choice:
Among the not-fully-persuaded: Many of the voters who supported New York Sen. Hillary Rodham Clinton in the Democratic primaries. Just under half, 47%, now say they back Obama and won't change their minds. One in five, 23%, say they're supporting Obama now but may switch. And 30% say they'll vote for McCain, another candidate or no one at all.
By Big Tent Democrat, speaking for me only