Des Moines, Iowa (CNN) -- After a year when the Republican presidential race became defined by debates and cable news chatter instead of retail politics and town hall meetings, Iowa seems primed, in the end, to reward the candidates who did things the old-fashioned way.
Three Republican candidates -- Ron Paul, Mitt Romney and Rick Santorum -- are on the cusp of grabbing a coveted top-three finish in Iowa, the leadoff caucus state, which rarely picks presidents but usually finds a way to whittle down the field of candidates.
A Des Moines Register poll of likely caucus-goers released late Saturday found Romney clinging to a narrow lead with 24%, followed by Paul at 22% and Santorum gaining steam at 15%.
They were trailed by former House Speaker Newt Gingrich at 12%, Texas Gov. Rick Perry at 11%, and Minnesota Rep. Michele Bachmann at 7%. Former Utah Gov. Jon Huntsman is not competing in Iowa.
The candidates who fall short of a top three or four finish in Iowa, depending on the margin of victory, may be forced to re-evaluate their campaigns.
"Iowa matters because we shrink the field," said Christopher Rants, a former Iowa House speaker and a Romney supporter. "We weed out those who can't make it. If you can't build a grass-roots network in Iowa, you don't deserve to be president."
Romney was a rare presence in Iowa throughout the year, instead focusing his public efforts on the friendlier turf of New Hampshire, but both he and Paul maintained the political organizations they built during their unsuccessful 2008 Iowa efforts.
Since then, Romney's team in Iowa has quietly kept in touch with the kind of mainstream, business-oriented Republicans he has been pursuing nationwide.
Paul's backers, many of them independents and disaffected Democrats drawn to the candidate's unabashed libertarianism, organized organically and opened campaign offices in even the most remote parts of the state.
Santorum, who is peaking late and at the ideal moment, began working the state back in 2009 with little money or infrastructure, but has since visited all 99 counties in the state and held more than 360 town hall meetings. His appeal lies largely with social conservatives.
Three different brands of Republicanism
The three candidates arrived at this point, just two days before the caucuses, in different ways -- and each White House hopeful represents a very different brand of Republicanism.
"I don't think it matters who wins it here," said Davenport-based GOP strategist Steve Grubbs. "The real issue is who wins that conservative spot coming out of Iowa. We are going to have a libertarian slot, a moderate one and a conservative one. And ultimately it's going to be Romney versus one of those conservatives."
For most of the year, the attention in Iowa focused on the battle to be that conservative alternative to Romney.
Taking cues from former Arkansas Gov. Mike Huckabee -- who rode of wave of support from evangelicals and home-school advocates to win the 2008 caucuses -- most of the Republican field worked aggressively from the outset of the Iowa race to appeal to grass-roots conservatives.
Polls suggest that about half of likely Republican caucus-goers identify themselves as evangelical or born-again Christians.
One of the first major events of the Iowa race was a banquet last March at a megachurch in Waukee sponsored by the Iowa Faith and Freedom Coalition.
But in a sign that most of the unsettled field wasn't prepared for an early and aggressive dive into Iowa, only five candidates showed up: Santorum, Gingrich, former pizza executive Herman Cain, former Louisiana Gov. Buddy Roemer, and former Minnesota Gov. Tim Pawlenty, who later dropped out of the race after he failed to catch fire in the state.
Heavyweights take a pass
Meanwhile, potential heavyweight candidates like Indiana Gov. Mitch Daniels, former Alaska Gov. Sarah Palin and Huckabee were still making up their minds about the race. They eventually took a pass.
And one candidate who would soon plant a flag in Iowa, Minnesota Rep. Michele Bachmann, was not yet in the race.
The first chapter in the battle for the hearts of Iowa conservatives began in the early summer, when the outspoken Bachmann caught on among tea party activists and social conservatives.
Her chief rival was the more mild-mannered Pawlenty, who had lined up a crew of talented GOP operatives and was pegging his presidential hopes to a strong showing in the caucuses.
They dueled in the cornfields of Iowa until mid-August, when nearly 17,000 party activists showed up at the Iowa Straw Poll in Ames.
A traditional test of campaign organization that is closely scrutinized by the media and Republican insiders, the straw poll dealt the former Minnesota governor a mortal blow.
Bachmann narrowly defeated Paul to win the contest, while Pawlenty finished in a distant third place.
Deflated and out of money, Pawlenty quit the race the next morning.
A different route to Iowa
That summer weekend was perhaps the strongest indicator yet that the traditional path to victory in Iowa -- hiring veteran staffers, lining up chairmen and chairwomen county by county, and hosting town hall meetings -- was no match for the intense but still unquantifiable grass-roots fervor that had taken hold of the GOP during the 2010 midterm cycle.
Discussions about taxes, abortion, national security and immigration were not taking place in church basements or Pizza Ranch restaurants.
Instead, they unfolded in a rapid-fire procession of presidential debates and in interviews on Fox News that were watched closely by the conservative base.
As a consequence, the ups and downs of the Iowa race began to mirror national trends -- a problem for candidates like Pawlenty and Santorum, who were depending on charming voters in their living rooms more than on television.
Romney, meanwhile, remained steady at or near the top of the polls in Iowa.
But as his more conservative rivals traveled from Sioux City to Des Moines to Cedar Rapids, invoking the Bible and touting their anti-abortion credentials, Romney kept a careful distance.
Wary of his 2008 experience, when he devoted enormous resources to Iowa only to come up short to Huckabee in a mortal blow to his campaign, Romney rarely strayed from New Hampshire, where social issues are less important to Republican and independent voters.
Romney sees opening among divided conservatives
As fall approached, though, the conservative wing of the party remained divided.
And with polls showing that Romney-friendly issues like debt and the economy were more pressing to Iowans than social issues, his advisers began to see an opening.
Soon, he had little choice but to step up his Iowa game.
Perry, a formidable politician with deep pockets and more executive experience than Romney, stopped making noise about running for president and formally jumped in the race.
With his larger-than-life Texas swagger and ability to speak freely about his Christian faith, Perry stomped all over Bachmann's momentum and forced Romney to readjust.
After Perry delivered a retail politics tour de force at the Iowa State Fair in August and then barnstormed through the state drawing huge crowds, Romney and his team realized the need to derail Perry in Iowa before he could win the caucuses and move on to other nominating states with a huge burst of momentum.
So Romney started traveling to Iowa more frequently. And he brought with him a salvo of attacks against Perry's immigration record and other conservative pockmarks on his "career politician" resume.
But the battles of the Republican race continued to play out on debate stages, and Perry later dealt himself a series of mortal blows on national television that tanked his standing in the polls.
Perry inflicts his own lethal wounds
His "oops" moment at a November debate in Michigan may have been the most devastating blow, but Perry's wounds were opened in Orlando in October, when he sharply fired back at Republicans who opposed his Texas bill giving in-state tuition to the children of illegal immigrants.
Opponents of the legislation don't "have a heart," he said.
Regard for Perry among Republican activists quickly disintegrated, and 48 hours later he lost a major Florida straw poll that had been his for the taking just days earlier.
The debates -- there have been more than a dozen -- continued to drive Republican sentiment in Iowa throughout the fall.
After Perry's collapse, conservatives searching for the anti-Romney moved to Cain, a charming former restaurant executive who hawked his catchy "9-9-9" tax plan in every debate.
But Cain seemed more interested in selling copies of his book than actually campaigning for president.
He rarely showed up in Iowa and refused to put together a grass-roots organization that could eventually help him in the caucuses.
Cain's blatant lack of foreign policy knowledge began to damage his candidacy, and he later dropped out of the race after being accused of sexual harassment by multiple women.
A cagey pol re-emerges
Into the void stepped Gingrich, whose campaign imploded earlier in the year under the weight of debt and the departure of most of his staff.
But he leveraged a series of punchy and policy-fluent debate performances into a late surge to the top of the polls once Cain disappeared.
Romney immediately pounced on Gingrich, a cagey pol and Romney's most serious threat since Perry joined the field.
A pro-Romney "super-PAC" -- a political action committee that can raise unlimited sums from donors but cannot coordinate with a campaign -- pumped more than $3 million worth of television ads into Iowa attacking Gingrich.
The campaigns of Paul and Perry spent similar sums on television trying to weaken Gingrich, while Bachmann and Santorum traveled across the state accusing Gingrich of being a lobbyist who once teamed up with Nancy Pelosi to fight global warming.
Soon, Iowa airwaves and mailboxes were cluttered with messages from campaigns and super-PACs, and almost half of the television ads were critical of Gingrich.
Gingrich chose to remain positive, but with attacks against him going unanswered, his momentum stalled.
Santorum gains momentum in closing days
The only option left for voters looking for a candidate other than Romney or Paul -- whose foreign policy views are largely out of step with mainstream Republicans -- was Santorum.
The former Pennsylvania senator, a staunch abortion foe, began picking up a series of endorsements from pastors and evangelical leaders in recent weeks, handing him momentum with social conservatives at exactly the right time.
Santorum's organizational muscle pales in comparison to that of Romney and Paul, but the Christian activists he has been courting often organize on their own, and appeared to be moving in his direction.
Suddenly, less than a week before Tuesday's caucuses, the groundwork that Santorum had been laying for almost two years looked like it might produce results.
The new Des Moines Register poll declared Santorum to be the candidate with momentum.
While Santorum finished third in the poll, a closer look shows that in the final two days of the four-day survey, Santorum leapfrogged Paul into second place behind Romney, trailing by a 24%-21% margin.
But even with just two days before the vote, the race is far from over.
More than 40% of caucus-goers surveyed in the poll said they could still change their minds.
And unlike primary states, a respectable showing in the caucuses in the closing days of the race depends heavily on organization and a campaign's ability to get their supporters to their local caucuses.
Perry's campaign, for instance, is bringing in almost 500 out-of-state volunteers and -- crucially -- has lined up over 1,500 "precinct leaders" to speak for the candidate at the 900 caucus locations on Tuesday evening.
As President Barack Obama learned in Iowa in 2008, momentum in the caucuses can translate into magic.
But a candidate with an aggressive ground game can reshape the race on caucus night, no matter what the polls say.
"An organized campaign makes sure they are taking care of their business," said Iowa Republican Party chairman Matthew Strawn. "The best example of organization on caucus night is who the candidates have as their surrogate speaker in their precincts. When you have a third of the electorate persuadable to change, the people they have standing up in each precinct for their candidate becomes real important."