My guess is that many democrat voters for obama have been more of an anti-clinton vote than a pro-obama vote.
The hillbill team have turned this primary into a highly polarizing dirt slinging,race-baiting fight to the death, and largely due to their tactics many democrat voters state openly that they will vote for McCain rather than vote for obama.
If hillbill gets the vp slot they will obviously do their best to turn their dirty tactics and underhanded methods against McCain so try to get a chance at the heart-beat away from the presidency position. It is not very likely that obama's fragile heart-beat will keep them away from the presidency for very long.
In the more likely even that hillbill is denied this vp slot since obama is probably a bit too clever (above room temperature IQ), then hillbill will have not incentive to do anything to assist obama and actually an incentive to deny him the presidency, if only from spite.
It does seem likely that McCain will pick up sufficient voters from democrat defects to significantly tilt the playing field in his favour for a presidential win.
