Donald Trump addresses a rally in Waterloo, Iowa, the US, on Monday. Picture: BLOOMBERG/PATRICK FALLON
Donald Trump addresses a rally in Waterloo, Iowa, the US, on Monday. Picture: BLOOMBERG/PATRICK FALLON

IOWA — Hours before Iowans have their say on Monday night on who they think should be the next US president, candidates crisscrossed the state in an attempt to turn out every single supporter.

As has been the case much of the past year, two figures will overshadow the others: Donald Trump among the Republicans, and Hillary Clinton for the Democrats. Both come into Iowa’s first-in-the-nation caucuses leading narrowly in a Bloomberg Politics/Des Moines Register Iowa Poll released over the weekend.

Both also face rivals — senator Ted Cruz of Texas for Mr Trump and Senator Bernie Sanders of Vermont for Ms Clinton — who analysts say could see a late surge of voter enthusiasm that may push them past their better-known opponents.

Even Mr Trump, the king of confidence, admitted to being "a little bit nervous" in an interview on ABC’s Good Morning America. At a rally later in the morning, he urged his supporters to caucus no matter what. "If the doctor says you cannot leave, I don’t care, get out of bed," he said. "You gotta do it."

Ms Clinton conceded on NBC’s Today that it has turned into a "tight race", though one that she can win if "the people who are committed to caucusing for me" show up. Volunteers for her campaign have been working hard on that count, knocking on 186,000 doors in the past three days, Mr Clinton said in West Des Moines.

Before noon Central time, Iowa Republican chairman Jeff Kaufmann said that he was surprised by the level of interest from party members, and how that might lead to a higher turnout on Monday night.

"Phone calls at the Republican Party of Iowa headquarters are absolutely unprecedented. I mean we’re looking at 100 an hour," Mr Kaufmann told The Washington Post. "Now obviously not all of that is tied to Donald Trump. There’s also a lot of these calls that are going to a variety of candidates but I think that’s a sign of the enthusiasm."

Earlier, Andy McGuire, who leads the Iowa Democratic Party, predicted: "It could be a late night, seeing how competitive it is."

The quaint, quirky and often-criticised tradition of the Iowa caucuses will play out in school gymnasiums, fire stations, community centres, and other meeting places and voters will render the first actual verdict of the 2016 presidential campaign.

A Trump win — once viewed as unthinkable for a man who has run the most unconventional presidential campaign in modern history — could propel him towards a Republican nomination that’s far from guaranteed, but also harder to stop. The billionaire real estate mogul holds a big lead in New Hampshire, where the first primary will be held eight days after Iowa.

"I believe that I will win states that the Republicans never put down as a possibility," Trump said at a Sunday rally in Sioux City. "We’re gonna run the table, folks."

For Clinton, a victory Monday would be vindication for her crushing third-place finish in 2008, the caucuses that set then-US Senator Barack Obama on a path to the White House.

In her closing argument on Sunday afternoon at a high school in Council Bluffs, Iowa, Ms Clinton asked Democrats to consider her lengthy public service resume when making their decisions. "I want to be the president for the struggling, the striving and the successful," she said. "Stick with me, stick with a plan, stick with experience."

The caucuses started at 7pm Iowa time, although results are not expected to start trickling in from the roughly 1,700 precincts until early on Tuesday. Beyond shaping the future for many of the candidates, including some who could drop out late Monday or Tuesday, the outcome will offer a snapshot on the national electoral mood and on traditional power centres, including Washington and Wall Street.

An additional factor looming over the state is a potential blizzard that could dampen turnout, especially in southwest Iowa where the storm is scheduled to arrive first.

Over the weekend, the campaigns deployed thousands of volunteers to knock on doors and make calls in an effort to shore up supporters and try to convince those who remain undecided or open to changing their minds. The intensity was boosted by the fact that for the first time in eight years Iowa’s caucuses are being contested on both sides of the political aisle.

"I think it’s going to be a record turnout, just judging from all the candidates we have and the turnout they’re getting at their rallies," governor Terry Branstad said in an interview on Sunday. "Then, you add the Trump factor, and that’s a whole new dimension that we haven’t had before. I think we’re going to shatter the record."

Mr Branstad, the state’s top Republican, is predicting 150,000 to 160,000 people will participate in his party’s caucuses. The past record for Republicans, set in 2012, was about 122,000.

On the Democratic side, Mr McGuire is predicting turnout of "somewhere between 120,000 and 240,000". The top of that range would bump up against the record of almost 240,000 in 2008.

If turnout did reach that level, most strategists believe it would translate into a good night for Sanders, a self-described democratic socialist who is trying to turn out college students and other younger voters who have been galvanized by his campaign.

Matt Strawn, a former Republican Party chairman in Iowa, said he’s also expecting record turnout on his side. If that does not happen, he said it could end up being a better night for Mr Cruz, who is closest to Mr Trump in the Iowa Poll.

"Anything that would exceed 140,000 or higher, you’re probably looking at a pretty good night for Donald Trump," he said. "Anything less than that would start looking like a more traditional caucus electorate and that’s where the Cruz organizational advantage kicks in. He’s got a coalition that’s built on people that caucus every four years, like it’s their job."

A bellwether Republicans will be watching is Sioux County, a party stronghold in northwest Iowa. "Cruz’s goose is cooked at that point, if Trump is doing well there," said Eric Woolson, a Republican strategist in Iowa who worked for Wisconsin Governor Scott Walker’s failed presidential bid.

Mr Woolson said he would not be surprised to see some of the candidates who have trailed far back in the polls to drop out, if the results show no success in Iowa. He specifically cited Santorum and former Arkansas governor Mike Huckabee, who won the 2008 Republican caucuses, and former Hewlett-Packard CE Carly Fiorina.

In 2012, former Representative Michele Bachmann dropped out of the race the morning after the caucuses, following a sixth-place finish. With the snow storm headed for the Des Moines area, where many of the candidates will spend their Monday evenings, Woolson predicted some may drop out even earlier than Bachmann did.

"I think it’s going to be awfully tough Tuesday morning, given the weather," he said. "Some people may be forced to accept reality a little sooner than usual, on Monday night, instead of Tuesday morning."