In my regular column, I talk about the debate as part of a larger problem this GOP primary contest has created for the party’s candidates. For now, a few observations:

1. Why the change from Saturday to Sunday? It could simply be that David Gregory invited more confrontation with his opening question, which ended up setting the tone. It could also be that Santorum, Gingrich and Huntsman realized that they had let Romney off the hook on Saturday and needed to redeem themselves. Or they may have decided that going on the attack would work better if done only once and figured that the last debate would leave the more lasting impression. In any event, it made for good theater and useful politics, delineating differences between the front-runner and his challengers in a way they had not been delineated before.

2. Romney showed some weaknesses that may be more than passing. Newt’s invitation to Romney to drop the “pious baloney” will stick, and Romney was utterly unpersuasive when he used faux innocence to try to explain why he didn’t run for reelection as governor of Massachusetts in 2006: “Run again? That would be about me.” I am not a cynic. I do believe politicians are motivated by more than just raw personal ambition. But the notion that a candidate is not at least partly “about me” is absurd. Of course Romney is partly about me — as are all of God’s flawed creatures. The notion that he didn’t run for reelection just because the campaign would have been about him is simply not credible. It was a great gotcha moment when Rick Santorum puckishly asked Romney if this meant that he would not run for reelection as president. Romney was so emphatic in saying he would seek reelection that he undercut his entire point.

3. Ron Paul was Romney’s ally on Saturday night, directing all his fire at Romney’s opponents and virtually none of it at Romney himself. The dynamic Gregory set up made that very difficult for Paul on Sunday morning. Santorum was very much on the defense against Paul on Saturday. Paul found his offensive gear on Sunday.

4. Jon Huntsman’s defense of his service as Obama’s ambassador to China was one of Sunday’s best moments and might have political impact — not necessarily in winning over Republican voters but in encouraging New Hampshire Independents to pick up Republican ballots and vote for Huntsman on Tuesday. The polls are all over the place about Huntsman. He gave himself a better chance of finishing second with what he did Sunday.

5. Rick Perry was actually pretty good. Obviously, my politics are very different from his, so this is a comment not on what he said but on how he said it. He knew what he was trying to do and he executed reasonably well. It made you wonder what might have happened if he had gotten his act together on debates earlier.

6. Will any of this make any difference in Tuesday’s voting? My guess is that Romney took a dent. But we will know more about whether this has any real meaning for Tuesday’s vote over the next 24 hours.