He was for the provision before he was against it.
McCane could be President if only he'd run as a Democrat.
That's my guess. If McCain doesn't get the Repub nod for President, and if the Dems maintain their Senate majority in 2008, he'll switch parties is my best guess.
He knows he's a liberal and so do we. They'll not offer him much unless they end up with a tied Senate in 2008, but at least he'll be part of the leadership if the dems hold their majority.