McCain is humiliating the Republican party and ensuring their catastrophic loss on purpose. Remember, the party has never liked him very much, and till Bush's presidency(oddly enough, as the two men hate each other), was never much of a party-line voter.
He's well aware too that to have someone his age in that office, with the stresses the next president will be facing, would be terrible for the country; he'd probably barely make it through a first term.
And anyway, would you want to be the one who has to mop up Bush's mess? Maybe they're all doing it on purpose.
"Eternity in the company of Beelzebub, and all of his hellish instruments of death, will be a picnic compared to five minutes with me & this pencil." --E. Blackadder, 1789 Questionable
words & pictures from John Linton Roberson