IMO, the sooner, the better. Specter and Lott can follow right behind him. Since the Senate majority has swung anyway, now is as good a time as any to flush the trash out of the Republican party. The general public has been conditioned to believe that bipartisanship and appealing to "moderates" are requisite traits necessary to engage in politics in this country. Our political system is necessarily an adversarial one, and I expect the pols that I elect to support the party platform, plank by plank.
McCain actually believes that he has a "mandate" to push through campaign finance reform, just because he won a few primaries. I am amazed that the GOP has been this patient with him. He should jump ship now and let the voters in Arizona deal with him at election time.