Let's leave aside for a moment the bitter exchanges that made this debate such a wild departure from the soporific roundtable in Nevada.
I want to pick up on Hillary Clinton's positioning herself as the insurgent in this race.
Ever since Iowa, she's been running as though she's behind. That may have been true for about four days in between the first caucuses and the first primaries, but it is certainly no longer the case.
She won a tremendous victory in New Hampshire, a squeaker in Nevada, and her national lead, though narrowed, has remained just that, a lead.
Yet having suffered the slings and arrows and indignities of frontrunner-dom for the better part of a year, Clinton seems to have no interest in resuming the mantle.
Indeed, she seems to be relishing no longer being seen as queen of the hill.
It has allowed her and her surrogates to unleash myriad attacks, some of them substantive, most of them slimy, on Obama.
It's really a neat bit of poll-position jujitsu, if you think about it -- to be simultaneously in the lead and playing the underdog at the same time.
Obama fans should blame their candidate for letting her get away with it.
Certainly, a frontrunner doesn't get away with the kind of mud that Clinton was slinging tonight. We heard from Hillary that Obama is a slumlord enriching Reagan lover who seeks to protect sex criminals and porno shops.
Her performance was angry and undignified, but it worked for her because both she and Obama have tacitly agreed to let the public see her as the feisty back-of-the-pack candidate whose not above fighting dirty to claw her way to the top.... of a mountain whose peak she never left.
This mind-trick worked wonders for her in Nevada, where, again, she fought with the kind of desperation that is only forgivable from one who is trying to topple a giant. And she's got the same mojo working in South Carolina, where she's now expected to lose.
It's now to the point that if Obama underperforms on Saturday, he could be toast by February 5.