In order for any GOP candidate to win, he or she will need to hold together the traditional Republican constituencies of taxpayers, military, Christians and small business plus add one new one. Without a new core constituency, the GOP cannot win a national election. Christie, Bush and Paul all have the capability to appeal to new constituencies, but each of them also has the potential to lose voters from the traditional base. Romney brings no one new to the party and he cannot hold the Christian vote. Cruz and Perry can hold most of the base but will antagonize people from new potential constituencies.
That leaves Walker, who I think is the best candidate on paper but untested on the national stage.
I like to imagine a whole different kind of GOP -- one that is youthful, vigorous and future-oriented, and that is why I support Paul. But I realize I am probably being unrealistic insofar as Paul's ability to hold the base together. So I hold out hope for Walker.
I almost never agree with OPapaDoc, but I do agree that we need a candidate with that "new car smell."