None of the candidates has the extensive get-out-the-vote network that helped former Arkansas Gov. Mike Huckabee win in 2008.
But Mitt Romney and Ron Paul have strengthened the organizations they had in place for their failed bids four years ago. The cash-strapped others, including Rick Santorum, have more modest efforts and are mostly relying on momentum to carry their supporters to the caucuses on what could be a chilly night.
"This isn't the Huckabee year," said Susan Geddes, a socially conservative Iowa activist and top staffer on that Republican's campaign.
With the race fluid, all the campaigns are working to ensure their backers vote at the caucuses, where turnout of 120,000 would break the record set in 2008. Volunteer armies already are knocking on countless doors and making countless phone calls to get Iowans to the community meetings where they will take the first step toward picking a president.
The candidates, themselves, are making final appeals as they canvass the state.
"If you can get out here in this cold and this wind and a little bit of rain coming down, then you can sure get out on Tuesday night and you can sure find a few people to bring with you," Romney told a crowd on a dreary Friday morning in West Des Moines.
Hours later in Waterloo, Rick Perry implored: "I need you to brave the weather. I need you to come out and support us. If you have my back on Tuesday, January the third, then I will have your back in Washington for the next four years."
It's about this time every four years that scores of Christian home-school activists, pastors and other cultural conservatives fan out across the state to corral people to caucus on behalf of their chosen candidate. This year, that coalition -- which lifted the late-charging outsider Huckabee to victory four years ago -- is dividing its support among many candidates, including Santorum, Perry, Newt Gingrich and Michele Bachmann. None of them have had the time or money necessary to build strong operations.
That leaves the two Republicans, Romney and Paul, who are leading in polls but aren't favorites of devout social conservatives, as the candidates in the best position to get their backers to the caucuses in the traditional way -- by relying on their grass-roots supporters and precinct captains. If either triumphs here, organization will be partly the reason.
Romney's Iowa headquarters, a former Blockbuster Video store near downtown, was abuzz Friday.
By noon, Jason Russett, of Des Moines, a Romney supporter from 2008, said he had called 60 people who have agreed to represent Romney in their precinct "in some fashion" to make sure they had packets that include a Romney campaign T-shirt and caucus-night talking points. About a dozen other volunteers were using laptops to auto-dial numbers in some of the state's 1,774 precincts.
Although he has a much smaller paid staff in Iowa than four years ago, Romney has relied heavily on volunteer assistance from top-level 2008 supporters. With a focus on retaining old supporters rather than recruiting new ones, Romney has spent the year quietly reconnecting with many of the roughly 30,000 Republicans who voted for him before. And he's armed with a voter database leftover from his last $10 million Iowa campaign, while all opponents but Paul have had to hurry to build theirs from scratch.
Romney stepped up his outreach to past supporters in recent days as polls showed him in contention.
He spent the week campaigning primarily in the eastern Iowa areas he won four years ago. Huge crowds turned out.
"If his turnout here this week is any indication, he's in very good shape here," Muscatine County GOP Chairman Mark LeRette, who supports Santorum, said of Romney. "He's the defending champ here. I expect him to win Muscatine County."
In more conservative parts of the state, Romney dispatched surrogates like South Dakota Sen. John Thune and had former Kansas Sen. Bob Dole, 88, dialing key activists in eastern Iowa. By video on Friday, Romney implored Iowans to show up Tuesday and vote for him.
Paul, for his part, has methodically built local support networks across the state and has hundreds of precinct-level leaders prepared to stand up and speak Tuesday on the Texas congressman's behalf. His team, which includes members of local and state GOP committees, has been executing a far more robust effort than when his small organization helped him finish fifth in 2008. Polls show more likely Iowa caucus-goers have been contacted by Paul's campaign than any other.
And the outreach is only just beginning.
In recent days, an influx of out-of-state volunteers, mainly college-age supporters, descended on the state to help as Paul's team dispatches local supporters to knock on doors and convene local meetings to encourage turnout. It's unclear whether Paul's popularity among younger voters will translate into votes. In 2004, Democrat Howard Dean attracted younger supporters, who ultimately failed to deliver for Dean on caucus night.
"Now, the key is personal touch," said Drew Ivers, Paul's Iowa campaign director. "Email is pretty lame, so are automated calls. What really counts is neighbor-to-neighbor contact."
But don't count on the candidate himself to do that. At events, Paul never asks for anyone's vote.
Santorum, meanwhile, could end up being the surprise.
The former Pennsylvania senator scoured Iowa for the past two years, testing the notion that building personal bonds with voters is the key to victory Tuesday -- even if there's little organization to back it up. He's begun to emerge in recent days as the preferred social conservative and, if evangelical backers and home-school activists spontaneously coalesce behind him in the coming days, strategists say he could win, even without much of an organization.
Perry, the Texas governor, is viewed by strategists as having an aggressive ground operation with the most staff. He's advertised most aggressively, spending more than $3 million on 12 TV ads since November. He's also advertising on Pandora, a popular Internet radio station in a show of his campaign's new-media savvy.
But Perry's late entry into the race in August has forced him to raise money and travel to other early states, slowing his ability to build grass-roots support in Iowa.
Gingrich, the former House speaker, always had a skeleton campaign in Iowa and struggled to build upon it when his support rose in November and early December. He had said he was hoping to mobilize supporters in part through online turnout efforts. But that never really materialized, and Gingrich has lost momentum after a barrage of attacks from Paul's campaign and Romney allies.
Still, more than 68 percent of likely caucus-goers in an NBC/Marist Poll this week say they have been contacted by Gingrich's campaign -- the same total as Romney's. Perry and Paul have higher contact rates.
Bachmann, the Minnesota congresswoman, is hardly a factor. She struggled to retain the support of the evangelical base that helped her win the August presidential straw poll in Iowa. Yet, she raced through Iowa's 99 counties in two weeks, making quick stops in order to shoot video being distributed by email to local activists this weekend.