That's Beinart's bet:
[P]recisely because Santorum has gotten so little scrutiny, it’s likely that his support will sink after he endures the barrage—from both Romney and the media—that will surely follow a strong showing in Iowa. Were Gingrich or Perry to run strong in Iowa, it would prove the resilience of their support. But if, as expected, Santorum beats them, it may just be because he hasn’t faced the assault that all the other major candidates have. And there’s a lot to assault. Voters don’t usually nominate presidential candidates who lose their Senate seats by 18 points.
The Dish 