Nate Silver keeps pointing out that it doesn't really matter whether Judd Gregg's replacement in the Senate is another Republican. After all, several Republican senators, notably Olympia Snowe and Susan Collins, have demonstrated more loyalty to the Democrats this session.
While true, this ignores an important point. We haven't had a cloture vote yet this year. That is, the ladies of Maine have not cast a pivotal vote -- the roll calls on which they voted with the Dems would have gone in the Dems' direction no matter how they voted.
In a cloture vote, with all 58 or 59 (assuming Franken gets seated) Dems voting aye, would Collins or Snowe really stand against their party? The cross-pressure would likely be terrific, with their increasingly liberal constituency pulling them toward the Dems and their increasingly disciplined party pulling them the other way. I'm not sure if the party leadership can offer anything or make any threat that would seem as credible and tangible as voters kicking them out of office, which has happened to many Republicans in New England of late, but they can sure try.