You can pretty much stick a fork in John McCain. His campaign manager, Terry Nelson, and chief strategist John Weaver just abandoned ship. On the heels of the news that McCain 2008 has a smaller bank account than Ron Paul 2008 (think about that for a second), I think it's pretty safe to say McCain is toast.
With the possible excepton of Gary Hart, I can't recall a presidential candidate going from front-runner (or at least well-respected contender) to laughingstock and failure in such a short period of time. It's really sort of impressive.