With just one day to go before the Iowa Republican caucus, the latest polls have led most observers to expect that there will be two big winners: Mitt Romney and Rick Santorum. But even if that turns out to be true, the big question that needs to be answered Tuesday night is whether or not Iowa will start the process of winnowing the GOP field.

It is on that uncertainty the fate of the leaders may hinge. If we assume Santorum does finish strong or even win the caucus outright by, in effect, winning the mini-primary of evangelical and social conservative voters over rivals Rick Perry and Michele Bachmann, his ability to mount an effective challenge to Romney will in no small measure depend on the willingness of those two to hang on in the race. Romney has benefited from the inability of conservatives to conclusively settle on a single “not Romney” candidate and looks to be in a strong position to cruise to the nomination no matter what the others do. If Bachmann and/or Perry were to quickly exit after poor showings, it might give Santorum a far better chance to give Romney a run for his money.

If we are to assume that Santorum emerges from Iowa as the strongest conservative in the race, that ought to put him into position to take advantage of Romney’s weakness and to start chipping away at his lead in the other early primaries before mounting an all-out push on Super Tuesday and the later states. But Santorum, who up until just a couple of weeks ago was at the bottom of the heap, has little money on hand and only a rudimentary campaign organization outside of Iowa, where he concentrated all of his efforts.

A win in Iowa or even a top-three finish will enable Santorum to proclaim himself as the true conservative alternative to Romney, especially if, as expected, Newt Gingrich sinks to fourth or worse. But the only way for Santorum to take advantage of his well-timed late surge is for the other conservatives in the race to drop out.

So long as Perry and even Bachmann stay in to crowd the field, it will be impossible for Santorum to get the traction he needs to mount a credible challenge to the frontrunner.

If Santorum does well tomorrow night and especially if he somehow manages to ride his late momentum to an upset win, his money problems will be lessened if not completely solved. But Santorum’s ability to put himself forward as a potential nominee will be severely undermined if he is still struggling to compete for the social conservative vote against Perry, Bachmann or even Gingrich. The longer the second tier candidates stay in the better it will be for Romney.

On that score, there seems little reason for Santorum to be encouraged. Though her candidacy and campaign appears to have crashed in the one state where she had a fighting chance, Bachmann is talking as if she’s in denial about her dismal prospects and may wait to drop out. Perry has more than enough cash to continue and may think he will do better in southern states. He may decide to stick around until Super Tuesday in March, complicating a Santorum push to consolidate conservative support. As for Gingrich, even though his hopes appear to be as dismal as those of Bachmann and Perry, we must assume that if he didn’t drop out last summer, he won’t quit now, especially if he can continue to participate in debates.

In Santorum’s favor is the fact that the proportional vote rules will make it difficult, if not impossible, for one candidate to score an early knockout. That’s exactly what Romney will be aiming at if he can squeak out a win in Iowa that would almost certainly be followed by an expected easy victory in New Hampshire. The primary/caucus schedule was created in order to foster a long, drawn-out race, and that will be Santorum’s goal. But the longer it takes for Santorum to consolidate conservative support, the easier it will be for Romney to stay ahead of him.