It's important to remember that Santorum is Catholic and would never bomb the Vatican.
Santorum would probably do like dozens of historical Catholic rulers and set up his own puppet antipope though. He's already on record not liking Francis.
Source? I've only heard positive stuff from him.
It's well documented that he hates him. I don't have wifi now, but I know the breeding like rabbits comment stirred up Rick. Also one of the gay things naturally. Possibly something related to immigration too, but that may have just been a left wing blog seeking to stir up trouble using Catholic teaching for the xenophobe.