One of the problems with senators as presidential candidates is that they usually have never run anything, so they are not well-suited for an executive role. That seems to have been part of the problem with McCain. There’s this passage from the New York Times today:

Aides said that the problems started to peak two weeks ago at a meeting with Mr. McCain and about 100 contributors in 100-degree weather at his home in Sedona, Ariz. It was just before that meeting, aides said, that Mr. McCain and his wife, Cindy, were told how bleak the campaign’s financial situation was.
They said the McCains were startled and enraged.
Aides said Mr. McCain expressed concern that the image of his campaign overspending would invite mockery from opponents at a time when he is attacking excessive government spending. One McCain associate said the senator expressed astonishment at the Sedona meeting that he had spent so much money without putting a single advertisement on television.
It was that gathering that led to the shakeup announced on Tuesday.

“Startled and enraged”? Did McCain really have no idea how much money his campaign was spending? And why not? Then there’s this from the end of the Martin/Allen story in the Politico:

Republicans who work with the campaign had long complained that there weren’t clear lines of authority — too many cooks, with voters and donors not liking the soup. Almost all crucial decisions wound up with McCain, a recipe for disaster in a fast-moving presidential campaign. “The campaign was run like a Senate office,” said someone who deals often with McCain. “That just doesn’t work.”