Frist has been cuckolded by the 7 RINOs. Think of them as his wife. He can claim that he isn't backing down but the little woman is sleeping with the enemy and there isn't a damned thing he can do about it. If he calls the confrontation, the RINOs go along with Reid as they have pledged to do. Frist can bluster all he wants, but all it does is ratchet up the pathetic factor.
No, Frist is running for President as is McCain. If he makes McCain vote with the Democrats, he has finished McCain as a Presidential Candidate. There is more going on here than just judicial nominees. . .politics is a multi-level chess game.
That's crude, but you nailed it. Frist is secure in knowing that the failure of the Constitutional Option can't be laid at his feet by enough people to matter. There's still enough Pubbies that don't realize that the true measure of leadership is not standing up and getting knocked back down when you know you'll lose, but standing up and staying up when all the pundits have written you off.