Do you think President Obama is “a nice guy, but just is [in] over his head,” or do you think the president is “utterly irrational”? You can probably guess the author of each of those assessments–Mitt Romney and Newt Gingrich, in that order. It’s one reason Gingrich emerged as such a threat to Romney: he’s not running to patronize the president or mentor him; he’s running to beat him.

Gingrich delivered this line at a mid-December candidates’ debate. It was probably the single best answer at a debate thus far, and it’s why Gingrich remains a threat: there will be two debates before next week’s New Hampshire primary, two before the South Carolina primary that follows it, and two before the crucial Florida primary after that.

Here’s the video of Gingrich’s home run:

Last night, by contrast, Gingrich summoned not congenial self-deprecation and restrained consternation at an overly ideological president in thrall to special interests, but a bitterness at Romney that is boiling over. Rick Santorum’s near-victory last night poses another problem on this count for Gingrich: Santorum’s speech after the votes were counted was not only positive, but possibly the best speech any GOP candidate has delivered yet this cycle.

Gingrich is a better debater than Santorum, so much is at stake for both this weekend, when there will be two debates. But if the contrast between the two leading “not-Romneys” goes in favor of Santorum, it will be because Santorum earned it, and because Gingrich stopped effectively reminding voters what this process is ultimately about.