some good insight here ...
[q]For the first six months of this presidential campaign, everything went wrong for John McCain, putting him in a position where to win the nomination, he needed just about everything else to go his way. And with the exception of the Michigan primary, that’s exactly what's happened. McCain can claim credit for some of it: He staked his campaign on the surge, for instance, and if Petraeus and Co. hadn’t succeeded in reducing the violence in Iraq, I can’t imagine that the press would have beat the drum for a McCain comeback as shamelessly as they did, or that moderate Republicans who dislike George W. Bush, the key McCain constituency, would have turned out for him in the numbers that they did. (In the counterfactual where the surge failed and the civil war spiraled out of control, it's easy to imagine the campaign turning into a two-man race between Romney and Rudy, with both emphasizing their Mr. Fix-It skills and promising to clean up the mess – Romney with managerial competence and Rudy with brute force – while Huck’s lack of foreign-policy experience and McCain’s association with the disaster left them both out of the money.)
But much of what's happened to make McCain the presumptive nominee has been luck, pure and simple. He was lucky, to begin with, that George W. Bush lacked an heir apparent – no Jeb, no Condi, no Dick Cheney – who could unite the movement establishment against him. He was lucky that Mitt Romney was a Mormon. He was lucky that Fred Thompson, a candidate who might have succeeded in rallying both social and economic conservatives against his various heresies, was out-campaigned by Mike Huckabee, whose appeal was ultimately too sectarian to make him a threat. He was lucky that Rudy Giuliani ran an inutterably lousy campaign. (More on this anon.) He was lucky that Mike Huckabee won Iowa; lucky that the media basically treated that win as a McCain victory (though obviously his skill in cultivating the press made a big difference, in that case and many others); lucky, as David Freddoso suggests, that Huckabee decided to campaign in New Hampshire and (taking my foolish advice) Michigan instead of going straight to South Carolina; lucky that Giuliani decided not to campaign in New Hampshire after Christmas; and lucky, finally, that Fred Thompson decided to go all in against Huckabee in South Carolina, thus delivering McCain the Palmetto State and with it Florida. And he was lucky, above all, that his strongest challenger was a guy that almost nobody liked – not the media, not his fellow candidates, and not enough of the voters, in the end.
http://rossdouthat.theatlantic.com/archives/2008/01/fortunes_favorite.php
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but, hey, if luck had to strike one of the Republicans, i'm glad it was McCain.