The Republican presidential candidates will clash Thursday night in their final "make-or-break" debate before Saturday's crucial South Carolina primary. Tension is rising in the race — Rick Perry ended his campaign hours before the debate and endorsed fellow conservative Newt Gingrich, who has said he must win South Carolina if he's to overtake frontrunner Mitt Romney. How might the debate tip Saturday's results? Here, four key factors to watch:

1. Can Romney stop Gingrich's momentum?
Newt Gingrich has chipped away at — and in some cases, erased — Mitt Romney's lead in South Carolina polls. To counter the surge, Romney's surrogates have suggested that Gingrich is an unreliable conservative who has been using "the language of the left" to attack Mitt. The debate in Charleston will be Romney's last big chance before Saturday's primary, says Matt Viser at The Boston Globe, to take Gingrich "down a few notches in an attempt to quickly sew up the GOP nomination." But Mitt should be wary of focusing his fire too directly on Newt, says Jonathan S. Tobin at Commentary. If Romney acts like "he no longer believes he has the nomination in the bag," voters might start to agree with him. As tempting as it may be, "a change of style would be disastrous" for Mitt.

2. Will Gingrich knock it out of the park again?
"Gingrich's closing pitch is founded on his debate performances," says John Dickerson at Slate. His widely praised showing on Monday, in the first of the state's two debates, sent him climbing in the polls. Indeed, when Newt said poor people need jobs, not handouts, says Tom Dotan at Neon Tommy, "the debate audience, which was hyped up like the old Arsenio Hall show, gave a raucous standing ovation. And the sounds of hands clapping revived Gingrich like Tinker Bell." Can he do it again Thursday?

3. Or will Newt's ex-wife bring him down?
After the CNN debate ends, ABC will air what's being billed as a "bombshell" interview with Newt's second ex-wife, Marianne — an interview it's been promoting all day. (The former Mrs. Gingrich says, among other things, that Newt wanted an "open marriage.") "No one should be surprised," says Tobin, "if Santorum, who had hoped to ride evangelical support to victory in South Carolina, doesn't stay away from Gingrich’s personal problems." In many ways, the voters "who would be most moved by [Marianne Gingrich's] views on her cheating ex-husband are already opposed to" Newt, says Jennifer Rubin at The Washington Post. But you never know. If this becomes an issue at the debate, "Gingrich risks losing wavering evangelicals and those voters who are preoccupied with electability."

4. Will all the candidates get a fair shake?
The worst performers in recent debates have been the moderators, says Rubin. ABC's George Stephanopoulos got smacked for his "contraception, evolution, and other make-them-look-like-yokels questions." Fox News, according to The New York Times, staged a "get Romney" debate, taking it upon itself to give conservatives a shot at taking down their moderate nemesis. The last time Thursday's host, CNN's John King, moderated a debate, he interrupted and cut off candidates, wasting "precious time" that could have been devoted to substance. Let's hope he can muster "a semblance of fairness" in Charleston, so the candidates can make their closing arguments in the "most decisive" debate before a potentially decisive primary.