What to watch in tonight's GOP debate

This is it: One last Republican presidential debate before voters (finally) begin the process of deciding which Republican will face off against President Obama in the general election.

The debates have been enormously influential in the 2012 election cycle, helping burst the bubble of a onetime frontrunner (Rick Perry) while catapulting a candidate from afterthought to the top of the polls (Newt Gingrich). Tonight's face-off in Des Moines is the last scheduled debate before both the January 3 Iowa caucuses and the holiday season, a time when families gather to celebrate - and, in many cases, talk politics.

This is the second debate since Gingrich became the frontrunner for the nomination, and he is sure to once again be a target for his rivals. Last time around, Gingrich largely fended off their attacks. But Gingrich's rivals have sharpened their critiques: Mitt Romney, his chief rival for the nomination, has been aggressively pushing the notion that Gingrich is a "zany," "unreliable conservative," someone who can't be trusted as the GOP's standard bearer. Expect him to hit that point repeatedly tonight in an effort to convince voters that Gingrich represents an unacceptable risk as a general election candidate.

Gingrich has repeatedly vowed to run a positive campaign, though he hasn't always followed through; it will be interesting to see if he lashes out in response to attacks tonight or tries to take the high road. Gingrich's professorial posture in early debates - when he wasn't being attacked - convinced voters to give him a second look; his task tonight will be not to say something to make them reevaluate that decision.

(At left, Brian Montopoli discusses fears that Newt Gingrich could be the second coming of Christine O'Donnell.)

Romney will be looking to land punches while also avoiding the sort of gaffe he made last time around, when his offer of a $10,000 betgenerated a torrent of negative headlines. Romney is a good debater but can seem uncomfortable when on the attack; if he can be convincingly aggressive against Gingrich, it will both diminish the frontrunner and help put to rest concerns among some Republicans that he won't take the fight to President Obama in a general election.

Then there are the candidates who have pinned all their hopes in Iowa: Michele Bachmann, Rick Santorum and Rick Perry. All three are campaigning aggressively in the Hawkeye State in the hope that a surprise victory there will give their sputtering campaigns a shot of momentum. Expect all three to try to appeal to evangelical voters, who dominate the GOP electorate in Iowa, and to name check towns and landmarks in the state in an effort to squeeze out a few more voters come January.

For Jon Huntsman, the debate is also a chance to appeal to key early state voters - not in Iowa, which he has written off, but in his make-or-break state of New Hampshire, which holds its primary January 10. Huntsman's campaign was buoyed by a new pollshowing him in third place in New Hampshire, and you can expect the former Utah governor to tailor his comments tonight to the Granite State's independent-minded Republican voters - and its independents, who can vote in the state's GOP primary. 

Then there's Ron Paul, for whom a victory in the Iowa caucuses is not out of the question. Paul has an excellent Iowa ground game and has been running anti-Gingrich ads in the state, and a recent CBS News/New York Times poll showed him essentially tied for second there. There's no mystery what the libertarian-leaning Texas lawmaker will say - as he noted in a Fox News interview Thursday, "I've been saying the same thing for 30 years and suddenly there is a lot more enthusiasm." Look for Paul to clash with his rivals on foreign aid and the U.S. military presence abroad as well as civil liberties issues at home - and to be greeted with rapturous applause from his passionate supporters, who are usually a boisterous presence in debate audiences.

The Fox News/Iowa Republican Party debate will take place from 9-11 p.m. Eastern Time. Check back to CBSNews.com during and after the event for our reports on the biggest moments of the night as well as our take on who had a good night - and who didn't.