DES MOINES, Iowa >> Candidates for the Republican presidential nomination crisscrossed the frigid fields and icy roads of Iowa on Sunday, pleading with would-be supporters to cast votes in the nation’s first nominating contest tonight despite bone-chilling temperatures.

After a yearlong marathon of campaign events and tens of millions of dollars spent on television ads and mailers, the race is closing in much the way it started: Former President Donald Trump is the odds-on favorite to win in Iowa, most likely by a significant margin.

In the final day before the state’s caucuses, the most unpredictable element of the contest remained the weather. Life-threatening cold — with wind chills as low as minus 40 degrees — scrambled the turnout calculations that campaigns are making about the fortitude of their coalitions. Typically, presidential candidates in Iowa boast about the enthusiasm of their supporters; in this race, caucusing could be a feat of physical endurance.

“You’re hardy people. We like hardy people,” Trump told a crowd of hundreds at a student center in Indianola for his only in-person event in the final weekend before the caucuses.

Even with subzero temperatures, dozens of Iowans lined up to see the former president, bundled up heavily to protect from stinging gusts. His campaign provided three heated coach buses to give some of those waiting a place to keep warm.Beyond the cold, the race was widely seen as a contest for second place between former Gov. Nikki Haley of South Carolina and Gov. Ron DeSantis of Florida, who are trying to position themselves as the chief challenger to Trump. Vivek Ramaswamy, a technology entrepreneur, has fallen to a distant fourth place in recent polls.

Yet the size of Trump’s expected victory will offer early hints about the breadth of his support within the Republican Party and will help determine how the coming weeks unfold.

The Trump campaign hopes a big victory in Iowa followed by another next week in New Hampshire will all but end the nominating contest, allowing him to avoid a drawn-out and expensive battle. Behind the scenes, Trump has fretted that his supporters will not show up because of complacency given his huge polling lead and the freezing conditions.

“Dress warmly tomorrow night,” Trump told attendees at his rally, urging them to bring friends and not let the weather keep them away. He said immediately, as if to allay their fears: “By the way, it’s all inside. Everything’s inside.”

Haley canceled a morning event in Dubuque after high winds prevented her from flying across the state. DeSantis said he expected fewer Iowans to caucus than in 2016, the last contested Republican primary in the state.

Reports of frozen gas pumps, stalled cars and semitrucks jackknifed off icy highways underscored the risky winter conditions. The National Weather Service warned of wind chills that could cause frostbite and hypothermia within 10 minutes.

The dangerous weather threatened to make an already unrepresentative electoral process even more sparsely attended. Only about 187,000 Iowans caucused for Republicans in 2016, about one-quarter of the party’s registered voters in the state and less than 10% of state’s more than 2 million voters.

Caucusing, an extended process that begins at 7 p.m., is more laborious than normal voting. There is no absentee or early voting, which complicates attendance for people working evening shifts and parents of young children.

Democrats have pushed Iowa later in their presidential nominating calendar, deemphasizing the state’s quirky electoral tradition.

In her final events, Haley focused on DeSantis, reflecting her strategy to position herself as the primary alternative to Trump as the race moves into New Hampshire, where recent polls show her closer to the former president.

“We need someone with not only executive experience,” she said, in a reference to the Florida governor. “We need an accountant to get our economy back on track, we need a military spouse who understands that we have to protect our military and prevent wars, and we need someone who understands the threats of our enemy and knows what it means to get respect in America.”

Sunday, Larry Hogan, the moderate former Republican governor of Maryland, threw his support behind her bid. He urged rivals of Trump to unify behind her, saying she was best positioned to coalesce support from the anti-Trump forces in the party.

“She has the potential of moving into second place, although it be at a distant second place, which gives her momentum heading into New Hampshire,” he said on CNN.

Trump also picked up a last-minute endorsement. After speaking for about an hour Sunday afternoon, he brought Gov. Doug Burgum of North Dakota — who until last month was one of the former president’s low-polling primary rivals — onstage, where Burgum endorsed him.

DeSantis, who has the largest field organization in the state, argued that the weather would give his campaign the advantage because of its superior ground game.

“We’ve built a great army here,” he said.

His campaign will offer rides to caucus sites.

“And yes,” Andrew Romeo, the campaign’s communications director, said in a text message, “if it means shoveling a driveway, we will do it.

A key poll released Saturday night by The Des Moines Register, NBC News and Mediacom showed Trump with the backing of 48% of likely caucusgoers. Haley was narrowly leading DeSantis in the race for second place, 20% to 16%.

Iowa voters were quick to dismiss the cold as an unpleasant but familiar fact of life, to be taken in multilayered stride.

“It’s just not a big deal, honestly,” said Laura Bestler, 55, who showed up at a barbecue restaurant Sunday afternoon to hear from Haley. “People who want Nikki to be the candidate will show up for her, despite the cold.”

As she spoke, Iowa’s junior senator, Joni Ernst, walked past. Did she think the historic cold would deter Republicans?

“Are you kidding?” she asked. “There are no snow days for caucuses here.”