Republican leaders know that if they crack down hard on Snowe, they risk pushing her and other wavering Republicans into the arms of the Democrats. So, instead, they’ll lobby their own intensely in order to keep the GOP united and force the Democrats to find 60 votes by themselves.

Shelby has assured Republicans that he won’t cross over on his own. He told POLITICO on Wednesday that he would “never support something as the lone Republican.”

But the same can’t be said of Snowe or Graham…

Graham said he’s pushing a climate bill because it could mean good business, and he chalked up a tough town hall Monday in Greenville, S.C., to fringe elements of his party.

“Probably two-thirds of the audience was Ron Paul supporters or Constitution Party members, so they’re not my base,” he said. “I don’t think I can explain anything to these people, and I’ve stopped trying.”