Well, the only base he could have would be evangelicals, and he's a Catholic and thus is about as likely to get the evangelical vote like Huckabee did as I am of being crowned King of England.
It's not 1960 anymore. Evangelicals might not like Catholics, but I highly doubt that'll be the main issue. I'm sure they like Catholics more than they like Mormons. And who look who the other candidates are: Romney (Mormon), Gingrich (Catholic), and Paul (crazy, though Baptist). Bachmann, Perry, and Cain got the first three tries as flavor of the month because they are Evangelicals, but those three have failed. I'm not saying Santorum is going to have a surge and while I agree that him being Catholic is a contributing factor, that's not really the reason.
Depends on the evangelical in question. If they want a crazy bible beater they can go for Bachmann and if they just want another Christian they can work with than they could accept Paul. But I still don't see them going for a Catholic (or a Mormon, for that matter).
