Presidential candidates are needy creatures, replete with requirements and cravings. For money. For endorsements. For top-shelf talent. For media attention. And also for less tangible inputs such as respect and even adoration. But the one thing any half-sane aspirant to the Oval Office desires above all is momentum: the sense that things are clicking, that the arc of the narrative is bending his way, that he’s being engulfed by an ineluctable aura of impending victory.

All of which explains why Newt Gingrich has been wearing such a big grin lately—for his sudden, shocking, surreal attainment of the Big Mo is now the Republicans’ main story line. Gingrich himself was telling friends as far back as October that he could feel the surge beginning, but it wasn’t until the first week of December that he could point to solid evidence to back up his premonition. According to a set of Time-CNN polls, Gingrich had seized commanding leads over Mitt Romney in three of the first four states to vote: 33 percent to 20 percent in Iowa, 43-20 in South Carolina, 48-25 in Florida. Arguably just as ominous for Romney, Gingrich was trailing him by a bare nine points in New Hampshire, both a must-win state and firewall for the former Massachusetts governor. Moreover, another set of surveys by Quinnipiac University found Gingrich thumping Romney equally thoroughly in Ohio and Pennsylvania, and faring nearly as well as him against President Obama—thus undermining the argument of Romney and his people that nominating Gingrich would spell doom for the GOP in a general election.

A full-bore Romney onslaught has now been unleashed—from every available angle, on every conceivable front—to take down the new front-runner in Iowa. Its effectiveness will be one of the decisive variables in the caucuses on January 3 (and beyond). But a number of other, less obvious factors will matter, too, in the Hawkeye State. Herewith, five of them, in no particular order:

1. Rick Perry’s Hail Mary. On December 14, the Texas governor will begin an epic, fourteen-day, 44-city bus tour of Iowa that will take him into every corner of the state. At the same time, Perry’s own team and the pro-Perry Make Us Great Again super-PAC have spent more than $5 million on TV ads in Iowa, more than any other candidate’s combined forces—though that supremacy may soon be challenged by the Romney campaign and its main super-PAC, which just made a $3.1 million ad buy there.

That Perry is going all-out in the caucuses is hardly a surprise; if he finishes in fourth place, where he currently stands in the polls, or worse, his candidacy will be all but over. What’s startling is that Perry, with his well-deserved reputation for slashing at his opponents’ jugulars, has wielded the blade against Gingrich or Romney in only one ad, instead running soft-focus positive spots about himself and his faith (and, of course, inveighing against gay soldiers and Obama’s supposed “war on religion”). But there is a method to this apparent madness: a calculation by Perry’s people that, if Romney and Gingrich go nuclear on each other, the governor might profit from the fallout, appealing to Iowan voters turned off by all the negativity. A long shot? Sure. But it could happen—and if it does, it will be Gingrich who suffers far more than Romney, as some hard-right voters shift to Perry.

2. Ron Paul’s potential. Let’s be frank from the outset about one thing: Under no imaginable circumstances short of a takeover of Earth by an Ayn Rand–worshiping species of space aliens will the libertarian Texas congressman be the Republican nominee. The level of support for his—admirably consistent yet all too often crackpot—views in the GOP makes that outcome simply impossible. Yet Paul, by all accounts, has run the best campaign in Iowa of this presidential cycle, with a solid field organization, not inconsiderable financial resources, and a deep connection to a die-hard base of voters. In 2008, Paul finished fifth in Iowa with just under 10 percent of the vote; today, he is polling at roughly double that total and is running just behind Romney, in third place.

If that’s where Paul winds up, his effect on the broader dynamics of the race will be minimal. But many savvy Iowa political hands believe his ceiling is higher. Should he overtake Romney and finish second, it would inflict a brutal blow to the latter, who has abandoned any pretense of not competing in Iowa, thus raising the stakes for himself there hugely. But if Gingrich and Romney annihilate each other and Paul emerges in first place on caucus night—an unlikely but by no means far-fetched scenario—the impact on Newt would be equally severe, so high are the expectations running currently that he will win Iowa in a canter.

3. Michele Bachmann’s motivations. For the ultracon Minnesota congresswoman, the high point of her campaign can be pinpointed precisely: August 13, the day she won the Ames straw poll. Since then, it has been all downhill for her, as her standing in Iowa has steadily declined from a high in the mid-twenties to around 7 percent right now. Of late, Bachmann has been regularly criticizing both Romney and Gingrich, but her attacks on the former speaker have been especially colorful and relentless. She has mugged him on immigration, saying he is “memory-­challenged” because of his past support of George W. Bush’s reform plan and the Dream Act. She has hammered him on buckraking, noting that “his address is located on the Rodeo Drive of Washington, which is K Street.” For the array of costly programs that he has supported in the past, she has dubbed him “a frugal socialist.”

The question is what Bachmann sees as her endgame. To some Republican professionals, the answer is obvious: She is trying to position herself as a top-flight contender to be Romney’s running mate. “Oh, she definitely wants to be his V.P.,” says one senior party strategist. “There is no other explanation.” If that is so, Bachmann could pose a particularly acute threat to Gingrich in the days ahead. As the only woman in the field—a position she has tried to exploit thematically, if only sporadically, in her campaign—and a hard-core religious rightster, she has unique standing to eviscerate the front-runner over his sordid personal history, and in a way that would be difficult for Gingrich to deflect adroitly.

4. Christian consolidation—or social-conservative splintering. Christian conservatives, meaning voters who describe themselves as Evangelical or born-again, have long constituted the most important voting bloc in the Iowa caucuses on the Republican side, making up fully 60 percent of the Iowa electorate. In some years, that bloc has coalesced definitively around one candidate, as was the case in 2008, when the Baptist minister and former Arkansas governor Mike Huckabee collected nearly half of its votes. This time around, however, the support of the Christian right has been split among a handful of runners: Bachmann, Perry, Rick Santorum, and now Newt Gingrich, who according to those numbers from Time and CNN has 31 percent of the self-identified born-again voters behind him, essentially in line with his overall total.

All along, it’s been widely assumed that a fractured Evangelical vote would be good news for Romney, and that may still hold true. But with Gingrich, a famously thrice-married Catholic convert, doing perfectly well with the Christian right and Romney doing notably poorly—carrying just 13 percent of that bloc, half the level of his support with the Republican electorate writ large—it raises the troubling specter that Romney’s Mormonism is inhibiting him severely in Iowa, just as some of his advisers have long feared. And that in turn suggests the possibility that if the Christian right does split itself largely among two candidates, say Gingrich and Perry, Romney could wind up finishing an absolutely disastrous fourth.

5. Double-barreled debate drama. Between this writing and caucus night, there remain two more Republican debates, both of them in Iowa: one hosted by ABC on December 10 and one by Fox News on December 15. By the time most readers clock this column, the first of those onstage wrangles will already have occurred. But predicting that the consequences of both will be significant requires no great prescience or imagination. In this presidential cycle, the debates have mattered more than ever; in a way, they have been where the Republican nomination fight has taken place. And these debates will be the most crucial of all so far, not only coming so close to the caucuses but being the first to take place when all the other candidates have an incentive to pile on Gingrich. If he emerges intact, there is a chance that nothing will be able to halt his momentum. But if he stumbles, things could get very interesting very fast, and maybe even downright weird. And in this weirdest of Republican nomination fights, what sensible person would predict anything else?

E-mail: jheilemann@gmail.com.