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.

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 bet generated 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.

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