Easy question. Are they going to, if so when, what will cause the defection? Or, are they going to stick around and become the two most powerful Republicans in the Senate?

Whatever the wingnut crazy base may say or how the GOP leadership might spin Specter's defection, the fact is that they know that the GOP can't afford more defections in the Senate. So I'd expect them to bend over backwards to keep Snowe and Collins in the fold. My guess is the Maine Senators just got way more powerful within their own party.