The McCain Option
Micky Kaus floats the idea of a McCain third-party run in 2008. I don't think that's likely to happen. McCain likes the spotlight he gets as the "maverick" Republican. As a candidate, that spotlight changes and suddenly he's not the spoiler or the dealmaker or the maverick, but a party leader who bears a lot of weight on his shoulders for positive action.
Still, it's fun to imagine. I'm sure the MoveOn, anti-Bush/War, Kennedy/Kerry/Dean part of the Democrats would love to push the "centrists" like Harold Ford Jr. -- the DLC / blue-dog Demcrats -- and the born-again moderates like Hillary Clinton over the side to purify their party's vision and message. That lops a good 10 to 15% of the electorate off their vote margin, but it makes them more able to push whatever message it is they want.
The danger is for the Republicans. Who goes with McCain? There's a broad swath of the party that is dissatisfied with Bush's performance as President as a conservative, and with Republicans in Congress who seem to be the Gang of Pigs Who Can't Shoot Straight. I doubt the libertarian wing goes with McCain; he seems to welcome government interference. Witness the horror that is McCain-Feingold campaign finance reform. The leaderships stays put, as that's where the pork and the money are. Do social conservatives go, hoping to bribe or bully McCain with promises of electoral support? I can't see that either.
Or do a lot of folks publicly support the Republicans, then quietly vote McCain on Election Day to punish the Republicans for forgetting who brought them to the dance?