Momentum gone. Dropping in the polls like a stone. Newt Gingrich's up, down, up, campaign is headed on the downswing - again.

Howard Fineman thinks there are 5 reasons for Newt's decline:

* The Palin Factor. Some D.C.-based establishment types were preparing to reconcile themselves to former House Speaker Gingrich, if not outright endorse him, before or after the South Carolina primary last week. But according to one such insider, who asked not to be identified because of her prominent corporate lobbying role, Gingrich fatally said on Jan. 18 -- three days before the primary -- that he would offer former Alaska Governor Sarah Palin a "major role in the next administration if I'm president." That one statement scared the accept-Newt, Republican-establishment types. "That sure did it for me, and I think for a lot of other people in town," the lobbyist said.

* The Rubio Factor. The popular Cuban-American senator from Florida has not endorsed a candidate, but he doesn't need to. He devastated Gingrich by complaining -- vehemently -- about an ad the Gingrich campaign had run calling Romney "the most anti-immigrant candidate," and implying that Romney had parroted the words of Fidel Castro. On Wednesday, Rubio denounced the ad as "inaccurate, inflammatory and doesn't belong in this campaign." The Gingrich camp withdrew the ad.

* The Moon Factor. A science-fiction fan and self-described "grandiose" thinker, Gingrich took it all too far when he vowed to establish an American space colony on the moon by the end of his second term. Even in Florida, where they love them some space exploration, it seemed an extravagant notion at a time when half the home mortgages in the state are under water. Former Massachusetts Gov. Romney, well prepared to capitalize, said that he would "fire" any staffer who brought him such an idea.

* The Wolf Factor. Gingrich was unable to bully his way past the savvy and imperturbable Wolf Blitzer as CNN moderator last night when the former speaker tried to decry the role of the mainstream media. And rather than lamely stand by in silence, Romney cleverly sided with Blitzer as he asked probing questions.

* The O'Donnell Factor. Debate coach Brett O'Donnell, formerly working for Rep. Michelle Bachmann (R-Minn.), earned his pay by coaching Romney in his answer about the role of faith in presidential decision-making. It was deftly pious without seeming to break the wall between church and state.

I would add that the candidate himself seemed strangely subdued in the last two debates. If he had shown the same amount of feistiness as he had in South Carolina - which is what Floridians were expecting - he might have weathered Romney's attacks better and maintained some momentum.

Now he is, according to the polls, dead in the water and even or slightly behind Romney going into Tuesday's primary. Romney is blitzing the air waves this weekend, burying Gingrich under an avalanche of paid media. Newt may yet win the primary. But any hope that the could have delivered a knockout blow to Romney in the Sunshine state is gone.