I secretly suspect that McCain doesn't really want the job, he's just stuck in it. Probably last spring, when he had some time to reflect while Obama and Clinton were still fighting, he realized he'd be spending a big chunk of his remaining years in the most unforgiving, demanding job in the world. At a time when it will almost assuredly be really rough in this country. The convention and Sarah Palin seemed to energize him for a time by letting him run the way he wanted to run, but now she has lost even some of her apologists (read
this National Review article if you haven't) and he's starting to get hammered in the polls and the press for saying one thing, doing another thing, then saying yet another thing. Which is what he has been doing his entire career, but it's never been scrutinized and he's never had to worry about holding onto conservatives.
Watching his run has been fascinating, because it has obliterated his entire image and public goodwill. Last fall, his campaign put together this fake future news article that talked about how McCain was able to beat Hillary because he stole the change issue away and ran a clean campaign. Which is either the saddest or funniest thing you've ever heard, depending on your opinion of hubris.