McCain's swing to the "negative" attacks directly against Barack Obama prior to the Republican National Convention are historically unprecedented, and contrary to the usual strategy for a candidate whose strategy for winning is to woo moderates to their side. These actions are consistent with the hypothesis that McCain may not be the eventual Republican nominee. A longer explication below.
It has become Common (Blog) Wisdom that John McCain has gone on the negative ad-hominem attack route. And quite early by all measures, with around 100 days left 'till the election, and both conventions, and several debates between now and then.
Usually, attack ads, and personal attacks against a candidate are intended to suppress turnout amongst the base of the targeted candidate. A side effect of a "negative campaign season", however, is to decrease turnout amongst all voters, especially independents. Conversely, positively themed ads are intended to boost turnout amongst the targeted candidate's base, and to win "new converts" over to increase what is considered a "base".
Standard strategy, therefore, is to stay positive for as long as possible, with some possible sniping from surrogates. Then, just before the actual election, to go massively negative. This builds the base as much as possible, then undercuts the other guy's turnout. Underdogs, of course, have a much stronger incentive to go negative, since presumably a leading candidate draws a larger share of their support from independents and leaning undecideds.
The risk for a candidate to go negative so far ahead of the election is that in so doing, they paint themselves as solely oppositional, and possibly drive down enthusiasm amongst their own base. It may be that John McCain, knowing he has little to lose on that front, has made a choice to do so. It might be that he is simply going unscripted, to his own detriment. Or, it might be because he has decided not to accept the nomination.
There has been some talk elsewhere, with people saying that there is a small, but nonzero chance that McCain might choose to withdraw his name just before or at the convention. They suggest that he can play the "health reasons" card at any time, given his age and history with cancer.
A quick check of the InTrade markets show that speculators are giving McCain a 96.5% chance of winning the GOP nomination. Considering that he has a strong lock on delegate votes (winner take all states in the GOP primaries ensure this), that means that the remaining 3.5% are either irrational, or betting on him stepping aside.
As an aside: these same markets give Obama a 96.3% chance. I would suspect that Obama's 3.7% is a combination of PUMA supporters throwing their money away, and people who are betting against him on the off chance (goodness forbid), that something terrible happen to him between now and the convention. But I'd rather not think about that.
In any case, if we acknowledge the possibility that McCain might withdraw from the nomination, his pattern of behavior suddenly looks much more plausible from a party-interested standpoint. As the "presumptive nominee", he has a platform to say whatever he would like, and get it reported on the nightly news. He can attack and keep on attacking, damaging his own party's enthusiasm for himself as a candidate, and sowing doubts amongst independents about Barack. Then, they pull a bait and switch, replacing him with Huckabee, and Romney as VP a few days before the convention.
Suddenly, the base is reenergized by the emergence of a new, evangelical candidate. The media has a field day talking about nothing but the new candidate for a solid couple of weeks. Barack's post-convention bounce is interrupted, and polls go crazy for a while until a new equilibrium is found. And, the Republican party hopes, the voters remember what that kindly old man said about Barack Obama before he had to withdraw. Because of cancer. And isn't he heroic? He was a war hero, don'cha know? And then he gave it all up for someone else.
Anyways, I don't think it is likely by any stretch of the imagination. John McCain doesn't strike me as much of a "team player," and it would be a massive gamble for the Republican Party to change horses in midstream. But this new behavior is consistent with this possibility, and I have to admit, that I would be more pessimistic about our chances as progressives facing a Huckabee/Romney ticket on election day than against McCain/whoever.