DES MOINES, IOWA—Tonight, tens of thousands of Iowans will begin the process of choosing the person who could be the next president of the United States.
...and that's about all that is certain at this point.
In the hours leading up to the first-in-the-nation caucus, there is still plenty of room for the winds to shift. In a Des Moines Register poll released last weekend, three candidates emerged as frontrunners: former Massachusetts Gov. Mitt Romney, with 25 percent of likely caucusgoers, Texas Rep. Ron Paul with 22 percent, and former Pennsylvania Sen. Rick Santorum with 15 percent. Yet the race remains remarkably fluid, as 41 percent of respondents said that they could still change their minds.
Many things might tip the scales for the winning candidate, but message won't be the deciding factor, says Mack Shelley, professor of political science at Iowa State University.
"I think the sales pitches have pretty well been solidified and run over and over," says Shelley. "Received wisdom tends to say it's all about the ground game at this point. It's a matter of who is going to be able to get his or her supporters out to the caucuses."
Candidates have spent the final days in last-minute get-out-the-vote efforts. Romney spent Monday holding a series of campaign rallies. Paul campaigned with his son, Kentucky Republican Sen. Rand Paul, on a "whistle-stop tour" of Iowa towns. Santorum held a series of meet-and-greets on his "Faith Family and Freedom Tour."
On the whole, getting out the vote isn't expected to be a struggle. Matt Strawn, the chair of the Iowa Republican Party, told NBC's Meet the Press on Sunday that the party has added 30,000 registered voters since the 2008 caucus' record turnout of 120,000.
That crowd of likely caucusgoers looks different from those that turned out in 2008. Ann Selzer, the president of Selzer & Co., which conducted the Register poll, noted on Saturday that the share of self-identified evangelicals among likely caucusgoers has decreased from 60 percent in 2008 to about one in three.
A smaller share of evangelicals may work in Romney's favor, says Shelley.
"Romney has a somewhat easier job than four years ago," he says, when Iowa's evangelicals coalesced around Huckabee, giving him a decisive win over Romney and the rest of the field.
But Santorum has momentum on his side. On the final day of the Register's four-day poll, 22 percent of likely caucusgoers chose him, just 1 point behind Romney. Santorum's groundswell of support has come at an excellent time—immediately before the caucuses, when there is little time for opponents to criticize him.
That momentum, says Shelley, is in part a product of evangelical Republicans flocking to him after having supported other candidates like Minnesota Rep. Michele Bachmann and Texas Gov. Rick Perry, as they seek out a candidate who "looks and sounds like a Huckabee." In addition, Santorum has spent far more time in Iowa than any other candidate, with more than 300 events—about 75 more than Bachmann.
Rick Cowman, a self-employed welding trainer from Monroe, Iowa, thinks that that facetime has helped Santorum. "I've texted with him—that's the kind of guy he is," he said at Monday's Newton event. After he met Cowman at a homeschool conference in June, Santorum called him to talk about their conversation.
"He cares about Iowans," said Cowman's wife, Dawn, a stay-at-home mom who homeschools their children.
It's not just Republicans who will make the difference on Tuesday; Iowa voters may register as a Republican on caucus day, meaning that independents could also influence the outcome.
Those independents will most likely support Paul, says Kedron Bardwell, chair of the political science department at Simpson College—it's just a question of how many come out.
"The one thing you don't know about Ron Paul supporters is exactly how many independents will show up at the site and register as republicans," says Bardwell. "They don't have any Democratic caucus to compete for their votes."
Those independents would add to Paul's rock-solid base of support, which helped him to a second-place finish in the August straw poll. Steve Payne, a homemaker from Des Moines, is an independent-turned-Republican who plans to cast his vote for Paul—even through the general election.
"If I have to, I'm probably going to write in Ron Paul [in November]," he said at a Ron Paul event Monday in Des Moines.
In addition to candidates' event appearances, campaign ads will certainly affect voters' choices.
Newt Gingrich has consistently spoken out against negative ad campaigns over the past week. A barrage of negative ads from opponents is credited with contributing to Gingrich's waning poll numbers.
Yet many voters say the recent glut of negative ads has had a counterproductive effect on them.
"The candidates don't need to be continually running each other down," said Wayne Burkhart of Woodward, who works for Costco, at a Sunday Gingrich event in Ames. The chair of his precinct, Burkhart is still undecided about whom to vote for, but says he is turned off by negative ads.
Still, says Bardwell, those ads are effective on the whole.
"There's a pretty strong consensus in political science that negative ads do work," he said.
Whatever eventually makes the difference, it won't be the weather. Today's forecast for much of Iowa features plenty of sun and above-average temperatures.