Mitt Romney's surrogates have started gong after Newt Gingrich, and it's not pretty:They're attacking Gingrich's spotty marital history, of course, but they're also saying he's erratic and untrustworthy.

Thing is, that's kind of true. I can't wait to see how Gingrich responds to these charges, because if he's having a bad day, his persecution complex and gigantic ego could turn this into something operatic. Saturday's debate could get interesting. If Gingrich manages to keep up a cool facade—even as he internally steams at these attacks—he might be able to dispel these charges before they have a chance to stick. But if he flips out in classic Gingrich fashion, his poll numbers could crater.

UPDATE: Bad news for Mitt Romney! Looks like Newt's showing a remarkable amount of discipline:

Newt Gingrich laughed off the Romney campaign’s attack on him for being too “irrational” and self-centered to be president, pledging that he would continue to run a positive campaign.

“We’re gonna stay positive. All I’m gonna say is, we’re gonna stay positive. We’re gonna stay solution-oriented and talk about what America needs to do. And the only opponent I have is Barack Obama,” Gingrich told reporters after an event in Greenville, S.C.