For the last several weeks, Newt Gingrich has gone out of his way to keep a positive message, making it a staple of his campaign strategy. It didn’t work — while Gingrich refused to go negative, Mitt Romney and his cohorts spent $4 million in three weeks to destroy the former Speaker, causing Gingrich’s support in the polls to plummet.

And so now it appears Gingrich is trying a new approach. His appearance on CBS’s “The Early Show” this morning is a must-see video.

The fireworks start about three minutes in, when CBS News chief White House correspondent Norah O’Donnell asked Gingrich about this recent comment: “Someone who will lie to you to get to be president will lie to you when they are president.” It led to this exchange:

“I have to ask you, are you calling Mitt Romney a liar?”

“Yes,” Gingrich replied.

“You’re calling Mitt Romney a liar?”

“Well, you seem shocked by it!” said Gingrich. “Yes.”

O’Donnell and co-host Bob Schieffer did, in fact, seem completely shocked that Gingrich was willing to say this on national television. That, in and of itself, is a shame — Romney has been lying uncontrollably for quite a long while. Paul Krugman a couple of weeks ago highlighted a series of blatant lies from Romney, and noted that the Republican presidential candidate “seems confident that he will pay no price for making stuff up,” in large part because we’ve entered an era of “post-truth politics.”

The question isn’t why Gingrich would say this; the question is why O’Donnell and Schieffer haven’t said the same thing.

In any case, Gingrich followed up on this exchange by launching an aggressive broadside against the likely GOP nominee, noting, among other things, Romney’s support for taxpayer-financed abortions, Romney distancing himself from Reagan, and Romney running to the left against Ted Kennedy.

“Which part of what I just said to you is false?” he asked the surprised hosts. “Why is it that if I’m candid in person and I wanted to be honest in person, that’s shocking? If [Romney’s] PAC buys millions of dollars in ads to say things that are false, that’s somehow the way Washington plays the game. Isn’t that exactly what’s sick about this country right now? Isn’t that what the American people are tired of?”

Oddly enough, those seem like pretty reasonable questions.

I don’t imagine Gingrich is going to do especially well when the dust settles in Iowa tonight, but if he sticks around for a while longer, I get the sense he’ll have plenty of interesting things to say about Romney in the coming weeks.

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Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.