Do you know for sure that he is going to vote that way?
If Brownback plans to run for President he will pay little attention to a tiny minority howling in the wilderness which could not get 10% of the votes if their beliefs were to be voted on. He is not going to ally himself with those attacking the President on every front.
Nor is he going to attack the nominee without cause. To do so would indicate that he does not have the Right STuff to be President.
Maybe someday people will wake up and realize that to be elected you must appeal to more than a minority of FR. We do not speak for the nation as a whole.
I would wager that not only will Brownback vote for Miers but so will EVERY GOP Senator. Her only opposition will come from the hard Left.