The race for the GOP presidential nomination has been a roller coaster ride, with one candidate after another surging and crashing. Of course, the race is still extremely fluid two weeks before Iowa kicks off the voting with its first-in-the-nation caucuses. But "the conventional wisdom still holds," says James Hohmann at Politico: "It's the top three on Jan. 3 who'll get to move on" past Iowa. The Hawkeye State "rarely chooses either party's nominee," says Chris Cillizza at The Washington Post, but "it has long served to winnow the field." In 2008, for instance, Democrats Joe Biden and Chris Dodd immediately dropped out after poor Iowa finishes. Recent polls show Ron Paul, Newt Gingrich, and Mitt Romney looking strongest in Iowa. Which GOP hopefuls will throw in the towel after the Jan. 3 caucuses? Here, four predictions:

1. Rick Santorum
The socially conservative former Pennsylvania senator has bet the farm on Iowa. "He has visited all 99 of Iowa's counties and courted every leading religious group in the state," says Sam Youngman at Reuters. "He has campaigned from sunrise to sundown in the diners, town halls, and community centers that are so crucial to the type of personal contact that Iowa voters have responded to for generations." But what worked for last cycle's Iowa winner — Mike Huckabee — isn't working for Santorum. He's "running no better than a distant fourth" in the polls, and "even if the top three stumble, it's questionable whether Santorum will be in position to take advantage." He needs a highly unlikely "top-two finish" to keep going, says Cillizza.

2. Michele Bachmann
After her victory in Iowa's much-hyped Ames Straw Poll in August, Hawkeye State native Bachmann "was the clear frontrunner for the Iowa caucuses," says The Washington Post's Cillizza. Then her poll numbers crashed. She seems to be recovering some lost ground with a pugnacious message about being a rare consistent conservative, but "she lacks the money to get that message out." Bottom line on Bachmann: "Without another obvious state where she can win, it's hard to see her as a relevant factor if she can't take first or second on Jan. 3."

3. Rick Perry
Perry has more money than Bachmann or Santorum, and he's barnstorming the state. But he hasn't clawed his way into the magic top three slots in the polls, says Politico's Hohmann. Without a "clear breakout" performance, Iowa could be Perry's "last stand." Voters in other states simply won't take him seriously if he winds up in fourth place or lower — and especially if he doesn't finish well ahead of Bachmann and Santorum.

4. No one
"Contrary to conventional wisdom and recent history, it's possible Iowa may do little to thin the herd of candidates," says Jennifer Rubin at The Washington Post. "Candidates who finish in the back of the pack" may still win 10 percent or more of the vote, and in a race this volatile, that's a good enough reason to keep going. And if a toxic crackpot like Paul wins, as seems eminently possible, "there is good reason for the entire field to throw up its collective hands, declare the contest irrelevant, and consider New Hampshire to be the first meaningful contest."