Voters listen to US Presidential candidates during a campaign event in Iowa. (AFP Photo)
US Republican and Democratic candidates made last-gasp appeals to Iowa voters Sunday, with their White House aspirations on the line in the first nominating contest of the 2016 campaign.
By late Monday, presidential hopefuls will learn whether the time, effort and money they poured into their campaigns have been rewarded with the kind of strong showing here that would lend huge momentum to their cause when the race shifts toward the next vote, in New Hampshire.
Republican Donald Trump and Democrat Hillary Clinton both were leading in the polls, but not by enough to assure victory for either candidate in Monday's caucuses.
Will an establishment Republican -- Marco Rubio, perhaps -- outperform the polls and make it a three-way race with Trump and conservative Ted Cruz?
And will self-declared Democratic Socialist Bernie Sanders convert the excitement about his political revolution into enough votes to upset Clinton's second shot at history?
Iowa, and the entire early momentum of the presidential race, is up for grabs.
Throwing a wrench in the works, forecasters say a major winter storm is brewing in the west, threatening to bring snow and a dangerous wintry mix to parts of Iowa just as residents are caucusing.
Armies of volunteers fanned out through the Midwestern state on the eve of the caucus, knocking on doors or manning phone banks to get out the vote, while candidates dominated the air waves with talk show appearances and a relentless barrage of campaign ads.
The three Democrats and 12 Republican candidates were hosting several dozen weekend events as they geared up for the vote.
Clinton, seeking to stave off a surge by Sanders, was leaving nothing to chance, stumping in the heartland this weekend.
Sanders, a Vermont senator, did the same. Speaking to a crowd of volunteers at his Marshalltown, Iowa field office, he declared his race with Clinton a "tossup."
A Bloomberg/Des Moines Register poll published late Saturday -- the final one of its kind this campaign season -- put Clinton just ahead of Sanders, 45 to 42 percent, within the four percent margin of error.
The same poll gave Trump a bigger lead over chief Republican rival Cruz, a senator from Texas.
The billionaire businessman had the support of 28 percent of voters, with Cruz at 23 percent.
Lurking in third was Senator Marco Rubio with 15 percent, and his trend has been on the rise in recent weeks.
If Rubio makes a strong showing in Iowa, he would emerge as the top mainstream Republican candidate heading into the New Hampshire vote on February 9.
Sanders has energized young Democrats with his denunciations of the "billionaire class" and his calls for a political revolution.
The thousands of students who fill his rallies could produce an upset, if they show up to caucus.
"If the turnout is high, I think we've got a real shot to win this," Sanders told CNN's "State of the Union" program.
The Sanders campaign said it raised more than $20 million in January, nearly doubling its previous fundraising pace and underscoring an ability to stay in the US race for the longer haul.
The Clinton team has yet to release January numbers. But she received a boost Sunday with a $6 million contribution to a pro-Clinton independent group from billionaire investor George Soros, The Hill newspaper reported.
Courting evangelicalsIn the Republican camp, Trump and Cruz made appeals to Iowa's many evangelical conservatives.
Cruz said he was praying for his rivals as he worshiped at an evangelical mega-church in West Des Moines, telling reporters he had prayed that "God's blessing and peace and love be upon them."
Trump made the requisite appeal to evangelicals, who are expected to play a huge role -- they comprised 57 percent of caucus voters in 2012.
But like other candidates Trump moved to soften Iowa expectations, telling CBS's Face the Nation, "I don't have to win it," even if "it would be really good."
Rubio, meanwhile, was seeking to cut into Cruz's standing, hammering him for what Rubio described as changing positions on immigration.
"He's not a consistent conservative, he's a political calculating one," Rubio said.
Long-shot hopefuls like Carly Fiorina and Mike Huckabee reminded voters that polls are notoriously unreliable in Iowa, where political upsets are commonplace.
Huckabee told a crowd at a West Des Moines coffee shop that he was counting on a "surprise" to propel him into the top tier.
"Tomorrow night is in God's hands," he told them, "and yours."