"The bad news keeps piling up for Newt Gingrich," says Amanda Paulson in The Christian Science Monitor. His double-digit lead in several national and Iowa-specific polls has evaporated, putting him neck-and-neck with Mitt Romney or, in one new PPP poll of Iowa, behind both Romney and Ron Paul. That PPP poll also has Gingrich's net favorability rating plummeting from +31 two weeks ago to -1 now. Many political junkies had thought Newt's rise to frontrunner status would be more permanent than the short-lived boomlets enjoyed by Michele Bachmann, Rick Perry, and Herman Cain. Why has Gingrich fallen so hard, so fast? Here, five theories:

1. Gingrich was buried under negative ads
The Gingrich campaign is pushing back against an onslaught of TV and radio ads attacking him in Iowa, but the former House speaker's new $242,000 ad buy may be too little, too late. Ron Paul has been hammering Newt for weeks as a phony conservative, and a pro-Romney super PAC has been outspending Gingrich 34 to 1. "The Romney-Paul onslaught is clearly generating a lot of heat, and Gingrich's waxen wings are melting underneath it," says Adam Sorensen at TIME. When you talk to Iowa's caucus-goers, you hear distinct echoes of the ads, says David Weigel at Slate. That proves the attacks are working.

2. GOP voters remembered Newt's many flaws
Many members of the media and the Republican establishment assumed that because they remember Gingrich's many vices, everyone else did, too, and accepted Newt anyway. Wrong, says Jennifer Rubin at The Washington Post. Many GOP voters needed a "refresher course in his erratic leadership, his bizarre schemes, and his ethics deficiencies." But once they got it, "the bloom came off the rose." For all the right-wing blog and "talk-radio-show set screams" about the GOP "elites" vs. the base, once Newt's faults "trickled down" to voters, "the base essentially came to agree with those 'elites.'"

3. Newt's attack on the judiciary backfired
Facing a hostile GOP establishment, Gingrich "apparently decided to make a radical, constitutionally dubious assault on federal judges — a favorite right-wing punching bag for decades — the centerpiece of his message," says Steve Kornacki at Salon. But that has only reinforced "whatever doubts rank-and-file Republicans have about his maturity, stability, and electability." Attacking "the only branch of government that enjoys almost 50 percent popular support" is a real head-scratcher, especially given the federal judiciary's recent conservative bent, says Dahlia Lithwick at Slate. It's "a distinct possibility that Newt, the big ideas man, never fully appreciated that the 'war on activist judges' is a talking point, not a position paper."

4. Republicans simply don't trust him
In the end, this wild boom-and-bust GOP primary race has been "a search for trust," says TIME's Sorensen. Already "tarred by a sketchy past," Gingrich's "brazenness" as the frontrunner has only eroded voters' confidence that he wouldn't "mess up what should be a favorable election year" for the GOP. That's why Romney's charge that Gingrich is too "zany" for primetime stings so badly. "Republicans voters trust that Romney can beat Obama," and even though they "hardly trust anything else about him," that might be enough for Mitt to seal the deal.

5. It's just Newt's time to crash and burn
Why is anyone surprised at Gingrich's "swift and sudden rise, followed by a sudden fall"? asks Doug Mataconis at Outside the Beltway. The real shocker would have been if he hadn't "followed the same path as all the other contenders that have arisen since this race started in earnest in August." Having failed to raise money or do anything else you need to do to actually run for president, "Newt's only chance was to catch his wave with less than a week before Iowa," says Noam Scheiber at The New Republic. "Anything else just wasn't going to work for him. And it didn't." He peaked too soon, and couldn't hit back when "the inevitable hazing came."