On Wednesday night, the four remaining Republican presidential candidates congregated in Mesa, Ariz., for their 20th, and likely last, debate. Mitt Romney, Rick Santorum, Newt Gingrich, and Ron Paul sat at side-by-side desks, while CNN moderator John King peppered them with questions on everything from foreign policy to congressional earmarks. But with pivotal votes looming — Arizona's and Michigan's primaries on Feb. 28, and make-or-break Super Tuesday on March 6 — much of the debate devolved into "fiercely combative" bickering. Here, five key takeaways:

1. Romney and Santorum really dislike each other
There may have been four candidates on stage, "but the main event was Santorum versus Romney," says Paul Begala at The Daily Beast. With Santorum, leading in most polls, enjoying frontrunner status, Romney did his best to reclaim the edge. Throughout the "painfully long and often personally biting" debate, says Maggie Haberman at Politico, "Romney and Santorum made clear their visceral dislike for the other." Each man "chuckled and smiled as the other spoke. They interrupted and talked over one another." And "Romney, especially, came off snippy, and at times a bit nasty."

2. In the end, Romney won
Snippy or not, Romney kept Santorum on the defensive all night, says Jennifer Rubin at The Washington Post. "Romney's staff must have worked overtime" digging up dirt on Santorum, including past subsidies for the airline and steel industries, a propensity for earmarking, and an endorsement for party-switcher Arlen Specter. Romney used it all to make Santorum sound like just "another weasely senator." The attacks flustered Santorum, says Michael Tomasky at The Daily Beast, and left him mumbling lawmaking minutia. Meanwhile, "Romney kept getting off soundbites," which is how you win the audience, and the debate.

3. Mitt got a big assist from Ron Paul
The Texan was mostly a non-factor in the debate — except when he paired up with Romney to double-team Santorum, says Politico's Haberman, at one point branding the Pennsylvanian a "fake conservative." This is a "role he's played in past debates, slamming Santorum almost whenever he could and joining Romney in piling on." No wonder Paul's "'bromance' with Romney is now an openly discussed fact of the 2012 campaign." Santorum certainly noticed, telling a reporter afterward that he should ask the two men "what they have going on together."

4. A suspiciously friendly audience helped Mitt, too
"Romney was buoyed, as he was in the Florida debates, by a crowd that favored him," says Politico's Haberman. The audience cheered Romney repeatedly, and Santorum "seemed to get ground down" by repeated booing. Romney clearly filled the room with supporters, says Will Wilkinson at The Economist, and his "success at hall-packing made him look like a winner." But offstage, in the real world, he's still "losing to Rick Freaking Santorum."

5. Newt floated above the fray... and out of the race?
"Gingrich didn't have a game-changing moment" in the debate, says Ginger Gibson at Politico. He attacked the media, of course, says Joe Gandelman at The Moderate Voice, but "half-heartedly," as if he knew prolonging the schtick would open him to ridicule, "like a comedian telling the same joke to the same room." It's clear Newt has "pretty much given up," says Michelle Cottle at The Daily Beast. "Gingrich the attack dog" was replaced by an "enthusiastic, vigorously nodding wingman," someone who is obviously angling for an advisory position should any of his rivals win in November.