S Republican and Democratic candidates made last-gasp appeals to Iowa voters just hours before the first nominating contest of the 2016 campaign, with their White House aspirations on the line.
By late today, 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 early momentum in 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 yesterday, 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.
Most of the 12 Republicans and three Democrats in the race were holding several weekend events to press the flesh and win over voters.
By evening, several leading candidates were rallying their faithful, pleading with them to defy snow or freezing rain and bring friends and neighbors to caucus.
Clinton, seeking to stave off a surge by Sanders, was leaving nothing to chance, stumping in the heartland this weekend and warning that the policy proposals of her main rival were pie-in-the-sky idealism.
"I don't think America can wait, I don't think it can wait for ideas that sound good on paper then can't go through the gridlock," Clinton told about 2,600 people at a rally in a Des Moines high school.
Sanders, a senator from Vermont, declared his race with Clinton a "tossup."
A Bloomberg/Des Moines Register poll published late Saturday put Clinton just ahead of Sanders in Iowa, 45 to 42 per cent, within the four per cent margin of error.
