With New Hampshire in the rearview mirror and Iowa practically ancient history, the four remaining GOP presidential candidates are scrambling for last-minute support in South Carolina, which will hold its primary on Saturday.

Will Mitt Romney or Newt Gingrich win? Can Ron Paul or Rick Santorum pull off an upset? Will anyone drop out afterward? And what will the results mean?

Here are five things to look for when the results come in.

5. The Super PAC Show

One of the defining aspects of this election has been the advent of independent expenditure-only committees, better known as super PACs, and with each caucus and primary, the controversy surrounding them has grown along with their influence.

In South Carolina, super PACs have spent more money on TV ads than the candidates themselves have, and 80 percent of the super PAC ads have been negative, according to the Campaign Media Analysis Group.

This has led to a great deal of bickering among the candidates, especially between Romney and Gingrich, over the merits of running a positive campaign, but there is no denying the impact super PAC ads have on public opinion.

These ads have accused Romney of destroying jobs while he was CEO of Bain Capital, Gingrich of being in the pocket of Freddie Mac and Santorum of supporting a bill to allow convicted felons to vote -- and the whole time, the candidates themselves have denied any accountability for the truth of those accusations.

In truth, super PACs have created a campaign climate in which it is nearly impossible for a positive campaign to be successful. The staying positive through Iowa, through $3.5 million of negative attacks -- you either have to unilaterally disarm and leave the race, or you have to at least bring up your opponent's record, Gingrich said at a debate in Myrtle Beach, S.C., on Monday.

It was a far cry from his earlier insistence that his campaign would never attack a fellow Republican, but it was a necessary acknowledgement of a new reality. The results of the South Carolina primary will give us more evidence of the impact of super PACs and of the candidates' newfound ability to distance themselves from the dirty work.

4. Paul Tempering Expectations

Ron Paul is unlikely to place as high in South Carolina as he did in Iowa or New Hampshire -- this particular primary is between Romney and Gingrich. This is in large part because, despite Paul's popularity among veterans, his cut-military-spending message does not resonate very well in a state with seven major military bases -- a reality seen when he was booed during the Myrtle Beach debate on Monday.

But a low finish here will not affect Paul very much in the long run, precisely because it is expected. He has not spent nearly as much time in South Carolina as he did in Iowa and New Hampshire or as he plans to do in upcoming caucus states like Nevada.

Paul has a defined strategy, and it does not involve wasting time in states where most voters are not receptive to his message or where, as in Florida, the winner takes all the delegates. Instead, he is focusing on states he knows he can win and states that allocate delegates proportionally, which allows him to collect delegates from second- and even third-place finishes.

He could pull out a third-place finish in South Carolina, because Santorum's poll numbers have fallen in the past few days, but it would be a distant third: he remains more than 15 percentage points behind Romney and Gingrich. Look for Paul to simply get through South Carolina en route to more promising states.

3. Romney in the South

It would be fair to say that Romney is unpopular in South Carolina. Nearly two-thirds of voters say they do not want him to be the Republican nominee -- and yet he is locked in a dead heat with Gingrich.

Romney's viability in South Carolina is probably less indicative of broadening appeal than it is of the internal discord among conservative voters and the growing sense of inevitability surrounding his candidacy.

You have some [evangelicals] that actually are for Mitt Romney because they've already made the leap that they are obsessed with defeating Barack Obama, Oran Smith, executive director of the socially conservative Palmetto Family Council, told the McClatchy news service.

But whatever the cause, a Romney victory would be a serious blow to conservative voters and leaders who still hope to derail his campaign, mainly because it would prove his ability to compete in the heart of the Deep South and the Bible Belt. A Gingrich victory, on the other hand, would show that Romney still has not managed to convince the evangelical and socially conservative voters who make up a large faction of the Republican Party that he is their man.

2. The Split Conservative Vote

Together, the two candidates who appeal most to social conservatives - Gingrich and Santorum -- have enough support to beat Romney in South Carolina. Apart, that's less certain. And if they don't beat him, the split conservative vote will have been the biggest factor.

Social conservatives do not like Romney, by and large, and they have more than enough clout to beat him in South Carolina, where 60 percent of voters identify as evangelical Christians. But this group -- though united by common stances on issues like abortion, same-sex marriage and, of course, religion -- is more ideologically diverse than most observers believe, and a split vote is almost guaranteed.

Conservative leaders are vacillating between electability and ideological purity, said Jamie Chandler, a political scientist at Hunter College in New York, and the social-conservative ideology itself is evolving as its adherents grapple with the fact that the public is moving gradually toward more moderate positions on social issues like same-sex marriage.

This makes it easier to understand why it has been so difficult for social conservatives or the evangelical bloc to coalesce around one candidate -- but it does not change the consequences of that indecision.

South Carolina may be conservative voters' last chance to put forward a consensus alternative to Romney. Whether they manage to do so will tell us a lot about where the race is going and whether Romney is beatable. It might just be the most important question of the night.

1. Winners and Losers

It was pretty much a given that Perry would finish last in South Carolina and drop out afterward. By dropping out two days before the primary, he took that non-story off the table.

Paul will almost certainly stay in the race through the Republican National Convention no matter what happens in South Carolina or any other state, so the remaining will-they-drop-out stories are Gingrich and Santorum.

Gingrich has said at least twice that South Carolina is a must-win state for him -- not only because the winner in South Carolina has gone on to win the Republican nomination in every election since 1980, but because after fourth-place finishes in Iowa and New Hampshire, it is his last chance to prove that he is a viable candidate.

His prospects look a lot better than they did even 24 hours ago. Insider Advantage and PPP polls released Thursday showed him leading Romney by 3 and 6 percentage points, respectively -- a huge improvement from earlier in the week, when polls showed Romney ahead by anywhere from 7 to 14 percentage points. Romney is leading the following primary state, Florida, by nearly 20 points, but if Gingrich wins South Carolina, there's no telling what momentum can do. At the very least, he would deny Romney a quick coronation.

Even in a must-win state, though, a close second would be enough to keep Gingrich's campaign going through Florida. Santorum is a very different story, and barring a sudden reversal in the polls in the next 48 hours, he is the most likely loser.

Rick Santorum's fortunes are on the wane, Chandler said. He received a small boost last Saturday from the endorsement of a group of evangelical leaders, but it is hard to say how many voters heard about that endorsement or how much clout it has. He also benefits from the news that he may actually have won Iowa by 34 votes, but if the South Carolina results show that conservative support is coalescing around Gingrich, that won't be enough for Santorum to justify staying in the race.