Gingrich sliding in Iowa polls

>> the biggest headlines in the final stretch is newt gingrich 's rapidly plunging support in iowa . tonight he's crunching his own numbers and sharing them with chuck todd . chuck joins us now from des moines . good evening, chuck.

>> reporter: good evening, lester . for the entire year the question hanging over the republican race is who is the alternative to mitt romney ? today we spent the day with the once surging newt gingrich who days ago looked like he locked up the anybody but romney slot but was now struggling. newt gingrich now acknowledging his slipping status in iowa making a case a close fourth would be enough. what do you have to do here?

>> you have to be in the up top three or four.

>> reporter: you have to win iowa or new hampshire?

>> and south carolina . every single one.

>> reporter: for gingrich it's the lone alternative to mitt romney , and romney is doing everything he can to keep the former speaker down here. today a telling exchange over romney 's health care mandate.

>> i knew he supported the plan in the past, and i believe he supported it until he got into the race this year. maybe before that he changed his view.

>> it's aamazing that everybody, heritage foundation , gingrich everybody has figured out mandates are bad and mitt romney stands there with mandates.

>> reporter: he restated the pledge to stay positive. we showed a mailing from a super pak that supports him.

>> mitt romney is the second most dangerous man in america. does that cross the line in your opinion?

>> i wouldn't call him the second most dangerous man in america. i'm happy to publicly urge them to not repeat that line in future mailings.

>> reporter: he expressed disappointment although republican colleagues critical of his tenure of speaker of the house .

>> it surprises me. it probably shouldn't have. i fully expected the left, and then i expected -- i really didn't expect people i'd been colleagues with, people i'd known for years to be as negative.

>> reporter: several times during the interview he linked himself to former president ronald reagan and compared his battle with romney to old battles with moderate republicans like george h.w. bush .

>> the fight with romney is exactly the fight reagan was in with the establishment in the '80s. it's amazing how none of the fault lines have changed.

>> reporter: one obstacle with gingrich with christian conservatives is his marital history. what's your relationship like with your ex-wives?

>> with my first wife, we have a relationship because we share two daughters and two grandchildren, and it's very up respectful on both sides.

>> reporter: your second wife?

>> we don't have a relationship.

>> reporter: if he doesn't get the republican nomination, would he consider running on someone else's ticket?

>> can't imagine you'd be asked?

>> no, i'm too stroj a personality. would you want to be a presidential nominee with he me as your vice presidential nominee ?

>> reporter: gingrich let us know that one of the reasons he didn't make the virginia ballot, lester , was he basically had bad staff work, he said, and that's what he's blaming it on.

>> chuck, he talks about it's important to be at least three or four in iowa . we saw that new poll out that shows him at four. does he have an explanation for that?

>> reporter: you know, he doesn't, but he has been already rejiggering expectations a little bit. check out those numbers. we did a little math here. you have romney and paul with their constituency bases and eat up 47% of the vote. the next four folks add up to 50, and that's the gingrich problem or it's the rick perry problem or the rick santorum problem or michele bachmann problem. the point is the conservative vote wlshgs it's the evangelical or hard core conservative votes, they are getting split up four ways, and that's why mitt romney is suddenly seeing an opportunity to actually win here. that's the game. if that conservative vote consolidates, romney would be in trouble, but it's not. lester .