“Now that [Texas Gov. Rick] Perry and [Minnesota Rep. Michele] Bachmann are out of the race, conservatives are attempting to rally around a single conservative candidate, the one who is most viable, and that’s Newt Gingrich,” said Walter Whetsell, a South Carolina-based Republican consultant.

Republican presidential candidate, former House Speaker Newt Gingrich, accompanied by his wife Callista, arrive as for visit to Children's Hospital, Friday, Jan. 20, 2012, in Charleston, S.C. (AP Photo/Matt Rourke)

Former Massachusetts governor Mitt Romney is the clear choice of the party establishment but remains unable to close the deal with the party’s conservative wing. That “no sale” has led conservatives on a nomadic quest that has, again, returned to Gingrich on the eve of South Carolina’s vote.

The reality of the South Carolina electorate for Romney is — and always has been — that he is probably capped out somewhere around 33 percent of the vote. That’s the percentage Arizona Sen. John McCain won in 2008 in South Carolina. It’s also consistent with the 30 percent (or so) of Palmetto State voters, who, according to knowledgeable political analysts, tend to prize electability over all other factors when choosing their candidate. That 30 to 33 percent will be with Romney almost no matter what. But expanding beyond it is very tough.

Thirty three percent was enough for McCain to win thanks to a split among conservatives between former Arkansas governor Mike Huckabee (30 percent) and former Tennessee senator Fred Thompson (16 percent) in 2008.

But with only four candidates left in the race now, Gingrich appears — if polling is to be trusted — to be coalescing enough of the conservative vote behind him go above Romney’s 33 percent ceiling.

The x factor in the “Gingrich as frontrunner” equation? Marianne Gingrich. The former Speaker’s second wife has alleged that he pushed her for an “open marriage”, allegations that have the potential to raise doubts in social conservatives’ minds about whether Gingrich truly is one of them.

While Gingrich forcefully pushed back on the “open marriage” question in Thursday night’s debate, it remains to be seen whether it changes the minds of many (or any) evangelical voters. “If Romney pulls this out, look carefully at the evangelical vote by gender,” said one Republican consultant who is familiar with South Carolina politics. “My guess is you’ll find a yawning gender gap on Gingrich.”

Below are our rankings of the likely order of finish in the South Carolina primary. How do you think it is going to turn out? The comments section awaits.

To the Line!

1. Newt Gingrich: The former House Speaker is currently in the midst of his second great comeback in this presidential race.

Gingrich is clearly the momentum candidate in the South Carolina field, meaning that he will likely pick up the votes of undecided conservatives. “The frontrunner’s support is so soft that all that really matters at this point is momentum,” said one GOP consultant who has spent considerable time in the state.

The key for Gingrich is for former Sen. Rick Santorum to fade just enough — maybe into the low teens — to allow him to win three in every five conservatives in the state. That’s about 39 percent, which would be enough to win.

2. Mitt Romney: There is still a path to victory for Romney in South Carolina although whether he can follow it is almost entirely out of his control.

Because Romney is capped in the neighborhood of 33 percent, he badly needs Santorum and even Texas Rep. Ron Paul to siphon off a not-insignificant number of anti-Romney votes from Gingrich to win.

The reality of South Carolina is that the electorate is just too conservative for Romney to win convincingly. He needs a split decision among the evangelical conservative vote to get across the line.

3. Ron Paul: Like Romney, Paul has a dedicated base of supporters who will, under no circumstances, leave his side. The problem for Paul is that his support base in South Carolina is roughly half the size of Romney’s.

Paul seems certain to get somewhere between 15 and 18 percent of the vote but growth seems unlikely — due, in no small part, to his foreign policy views, which don’t fit well in this military-heavy state.

4. Rick Santorum: On paper, Santorum’s unimpeachable social conservative credentials and strong ties to the religious community should have made him an appealing candidate in South Carolina.

But, races aren’t run on paper and Santorum just hasn’t really caught on. He’s been eclipsed in the past two debates by the more charismatic Gingrich and even though Santorum made a convincing case against the risk of conservatives putting their eggs in the former Speaker’s basket, polling suggests it won’t matter.

The question for Santorum is what he does next if he finishes last in South Carolina and Gingrich wins it. There will be considerable pressure for Santorum to drop from the race in hopes of uniting conservatives behind Gingrich as their best, last hope against Romney.