As I understand it, not being American, is that McCain was damned if he did and damned if he did not. He needed to mobilize the core voters on the right and the religeous right - without their organisations and volunteering, especially from conservative churches, he does not have the manpower resources to get his voters out to vote. As voting turnout is so low, it is as important to get the core voters out there voting as it is to attract the middle.
Core voters tend to be dissapointed and focus on the things they did not get and what was wrong after eight years with the same party. So McCain moved right and focused on social conservative issues to get his core voters out, but in doing that he lost the middle. I don't think his choice in Vice Presidental Candidate helped either. Palin seemed (and still seem) far out of her legue, IMHO.
McCain would need something that could give him the core without him moving right (a good Vice Presidental Candidate could do it), more money to match Obama's "every state" strategy and probably some kind of mistake from the Obama camp in order to win. I wonder if he could win at all, but it would certainly be a much closer thing than OTL.