Forf starters, he'll be rather old ( and he's no Reagan !), his cancer keeps coming back, most GOPers and ALL Conservatives hate the CFR Bill, and Senators have a lousy track record running for president! Oh yes, and the RNC isn't enamored of McLane at all, so they aren't going to help him at all.
Well, his age does work against him, though his cancer hasn't returned for a couple of years.
If McCain ran against Hillary, a Senator would win the presidency, for sure.
The RNC will support whoever wins the primaries. If McCain were to win, he would have all the support from the RNC he needed.
Who do you think makes up the RNC?