But the main event was the scripted Rick Perry attack on Romney, reprising the old charge that Romney hired illegal immigrants. Perry's face-to-face accusation of rank hypocrisy had the intended effect. From the ensuing melee emerged a singularity: a ruffled Romney, face flushed, voice raised.
Apples and oranges
It lasted just a millisecond, but it left its mark. The reassuring and unflappable command that had carried Romney through - indeed, above - previous debates was punctured. True, his unflappability is, to some, less reassurance than a sign of inauthenticity. But if you are going to show real passion, petulance is not the way to do it.
Worse, Romney turned to the referee - moderator Anderson Cooper - with a plaintive "Anderson?" seeking intervention. An uncharacteristically weak moment. What does he do when Vladimir Putin sticks a finger in his chest and starts yelling at a Vienna summit? Call for Anderson?
On substance, Romney remained as solid as ever, showing by far the most mastery of policy, with the possible exception of Gingrich - but without the lecturing tone and world-weary condescension.
Romney's command was best seen in his takedown of Cain's "9-9-9" plan. Cain refused to concede the burden to consumers of a national sales tax added on to existing state sales taxes. Doggedly sticking to his point long after it had been undermined, he kept raining down metaphors about apples and oranges. His national sales tax is a solution to a federal problem (the monstrous tax code), he insisted, and therefore irrelevant to any discussion of state sales taxes, which would exist regardless.
It took Romney one sentence to expose the sophistry. He simply pointed out that a real-world consumer with a basketful of apples and oranges would be paying the sum of the two sales taxes at checkout. Q.E.D.
Cain remained, as always, charming, engaging, confident, and good-willed, the only person on stage other than Bachmann who didn't have a sour or nasty moment. But his tax plan collapsed under fire in about 10 minutes, the coup de grace being delivered by Gingrich, who, when asked why the Cain plan is a hard sell, replied, "You just watched it." It was the deadliest line of the night.
However, the principal drama was provided by Perry. His aggressive performance brought him back into the game, especially because he now has a few weeks before the next debate to deploy his major assets: a talent for retail politics and a ton of money.
But the price of reentry was high. His awakening wasn't very pretty. He showed he can draw blood, but it was a nasty schoolyard punch-up.
In primary races, personal attacks often have the effect of diminishing both candidates. This happened in Iowa in 2004, when Democratic front-runners Dick Gephardt and Howard Dean knocked each other silly, allowing John Kerry and John Edwards to sneak past them.
Nonetheless, because of his considerable resources, Perry, by merely stirring himself, is back. But he hasn't solved his problem. It's not just that, as he readily admits, he's not very good at debating, although that in itself is a huge liability. It wasn't before 1960; it is now. And based on Perry's first five performances, President Obama would eat him alive in a one-on-one.
Bigger than Dallas
But apart from the importance of debating itself, Perry's often clueless responses betray an even deeper problem: He simply hasn't thought through the issues on a national scale. He is still Texas. And Texas simply isn't enough.
That was most glaringly evident during the Dartmouth debate when, in response to questions about China and then about health care, Perry sought immediate refuge by talking instead about his energy plan. Interesting, but unrelated.
The Las Vegas fight mildly unsettled the Republican race. But its central dynamic remains. It awaits the coalescence of anti-Romney sentiment around one challenger. Until and unless that happens, it's Romney's race to lose.
Charles Krauthammer is a Washington Post columnist.
He can be reached at firstname.lastname@example.org.