Last night on ABC, none of the Republican candidates seemed very interested in attacking Mitt Romney in person. This morning, NBC moderator David Gregory didn’t give them any choice: The first three questions, and the first 15 minutes of the debate, were devoted to Gregory begging the candidates to attack the front-runner. What did they show? That a few attack lines in a debate aren’t going to change the structure of the nomination race.

So, how did the candidates do this time? I’ll take them one-by-one:

Mitt Romney: While he took some hits, he showed again that he’s become pretty good at this; in most cases, he deflected them and continued on without much noticeable damage. Part of this is because the attacks that seem to animate Newt Gingrich the most — that Romney is much more of a politician than his rhetoric would have it, and that his super PAC ran unfair ads about the former Speaker — are probably not nearly as dangerous for Romney as issue-based attacks would be. I don’t particularly think that Romney’s style is all that appealing, but he’s much better at presidential debates than the others, and that helps. It also helps him, at least on stage, that as we’ve seen before (on jobs numbers, on Barack Obama’s mythical “apology tour” he’s not even slightly slowed down by facts.

Rick Santorum: Still not very good at playing at this level. Someone needs to tell him to just never again mention his own electoral history (no one cares, Rick) and to spend a lot less time on senator-speak. He actually has a message that should play well in GOP primaries (outrageous hawkishness in foreign affairs and extremism on social issues); he should just pound, pound, pound on that “positive” message, instead of getting stuck in the swamps of which bills he co-sponsored and the partisan breakdown of his House district in the 1990s.

Ron Paul: Not much to say. He does what he does. He’s going to get his percentage; he’s not going to be the nominee. This morning’s debate was no different, although it was interesting that Paul — who last night reminded us that he’s quite vicious on attack when he chooses to be — ducked Gregory’s invitation to go after Romney.

Newt Gingrich: See Romney comment. He started slow again this morning, but when the things that apparently really bother him came up, he hit Romney hard. Missed a chance, however, to attack Gregory for inviting GOP fratricide and praising himself for running a positive campaign before attacking Romney.

Jon Huntsman: Like Gingrich, appeared to be operating on personal slights in attacking Romney instead of executing a campaign strategy. His weird mix of praising bipartisanship along with Congress-bashing and embrace of some of the more extreme policy proposals just doesn’t work very well to my ears.

Rick Perry: Got one terrific line off mocking his own ill-fated “three agencies” blunder. Also called Barack Obama a socialist and said that members of Congress should be shot on sight. Okay, not that last one. He’s just fine at this now, by the way, probably a bit better than Santorum or Huntsman, although as an also-ran he rarely gets chances to speak.

Presumably few watched either debate this weekend, so the real question is how the spin goes, especially on news outlets New Hampshire and South Carolina voters will be watching. But as a guess, it’s hard to see that anything changed, which is of course just fine with Mitt Romney.