To follow up on my earlier post, McCain's difficulties as frontrunner are not without precedent. Mike Huckabee has been comparing himself to Ronald Reagan in 1976, and the comparison isn't a bad one, although Huck's got a ways to go. Reagan mounted a conservative challenge to moderate incumbent Gerald Ford that year right up into the convention, where Ford narrowly won with 1,187 delegates to Reagan's 1,070. Reagan went so far as to announce a vice presidential candidate and even attempted to woo delegates at the convention, with Ford counter-wooing by offering rides on Air Force One.
The rest, as they say, is history. Ford loses the general election, but Reagan is in the key position as the conservative that the party should have turned to to avoid the loss. This analogy would explain why Huckabee hasn't dropped out yet. He's not playing for 2008; he's playing for 2012.