My guess is that after the 2000 election, McCain was understandably at odds with President Bush; like most Senators, he has friends on the other side of the aisle and probably did grumble to them about the Bush administration. In early 2001, the Democrats were desperate to convince a Republican to change parties, and McCain, as the loser to Bush in the 2000 primaries, was a natural choice.I really don't care if he considered changing parties or not. I like the people in the middle, like Joe Lieberman, who could fit — but only uncomfortably — into either party. I'm that way myself.
With hindsight, the thought of McCain in the Democratic Party is ludicrous. Imagine a pro-life Joe Lieberman, and you're still only part way there. Given the way the Democrats have abandoned the war effort both in Iraq and globally, whatever grievances McCain has had against the Bush administration over the years are relatiely insignificant.
Am I the only one who can realistically picture myself voting for Clinton, Obama, Romney, or McCain?