Santorum, meanwhile, gives every impression of being a flavor of the week who happened to hit at just the right time for a surprise in Iowa. If Iowa had happened a week earlier, it would've been Paul with 25%. Two weeks before that, it would've been Gingrich. I expect Santorum to do reasonably well (15%? 20%?) in New Hampshire but just not have the funding or infrastructure to maintain a run beyond that. He could do okay in South Carolina, but Rick Perry's decision to compete there means the Evangelical vote will be largely split, providing a big help to Romney.
All this said, Romney is a very curious candidate. I can't think of a previous presidential candidate with such an enormous advantage in insider support who was nonetheless so despised by such a substantial chunk of his party. (Hubert Humphrey? Maybe, but he at least had an impressive track record on issues like civil rights that might have reassured liberal activists in 1968. Romney has no such goodwill among conservative activists.) The question is what that means for this year. My impression has been that conservatives will largely suck it up. Despite their misgivings about Romney's faith and his pretty recent liberalism, they will come to view him as far superior to four more years of Obama, and they will turn out for him. Some Republicans tell me otherwise, though. Will Evangelical activists stay home? Will Tea Partiers back a third party candidate? What if Ron Paul runs as a Libertarian or on the Americans Elect ticket? Yeah, that could mess up the election for Republicans big time.