This year, the Iowa Republican Caucuses will take place at 7pm on Monday, January 15 (local time) and any registered member over the age of 18 can participate.

The process is pretty straightforward: once participants have checked in, they elect a chair and a secretary to lead the meeting. After the American pledge of allegiance, a prayer, and a few speeches on behalf of the candidates, they’ll get a blank slip of paper to write down their presidential preference.

“Our country is angry. It’s divided. It’s accomplishing little and it is leading our citizens to be exhausted.”

Chris Christie, former anti-Trump Republican candidate

The ballots are immediately tallied in the same room, read aloud, and sent back to the state party. Republican officials say they expect results to start arriving about 8.30pm local time, and most precincts will be reported by about 9.30pm.

It’s worth noting, however, that this year’s caucuses will focus solely on Trump and his Republican rivals. While Democrats will start to hold their caucuses on the same day as Republicans, the results won’t be known until March.

That’s because the party changed its primary schedule, under Biden’s recommendation, to make South Carolina its first primary reporting state.

Why do they matter?

As the first state in the nation to cast votes for the 2024 election year, Iowa provides an early barometer of how politicians are resonating on the ground.

Presidential hopefuls often plough big money into advertising and spend months wooing voters, usually ratcheting up their campaigns at the famous Iowa State Fair in August, which gives them an opportunity to talk to locals while showing off their barbecue skills or posing for photos with mouthfuls of meat (a rite of passage for presidential hopefuls).

Perform poorly in Iowa and it can be debilitating. Do well, and it can spark what George H W Bush dubbed the “Big Mo” after winning Iowa in 1980: “momentum” for subsequent primaries in other early voting states, such as New Hampshire and South Carolina.

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When then-senator Barack Obama won Iowa in 2008, for instance, he shocked the political establishment and suddenly became competitive with Hillary Clinton in the national polls. A few months and several primaries later, he won the White House.

Who are the candidates?

Trump isn’t the only candidate to be running for president this year, but he’s certainly the GOP’s most dominant force – despite facing a whopping 91 criminal charges accusing him of subverting the last election, mishandling classified documents and paying hush money to a porn star. The former president denies all the charges.

His biggest rivals are Florida Governor Ron DeSantis and Trump’s former UN ambassador Nikki Haley, both of whom have been battling it out for weeks for as they seek to present themselves as the leading alternative to the Republican frontrunner.

DeSantis hopes he has the edge, having spent months campaigning in every one of Iowa’s 99 counties and gaining the endorsements of two of the state’s most influential political figures: Evangelical powerbroker Bob Vander Plaats and Iowa Governor Kim Reynolds.

However, Haley has been surging so much in the polls – particularly in New Hampshire, which holds its primary race a week later – that even Trump insiders seem slightly nervous.

The decision by anti-Trump candidate Chris Christie to drop out of the contest on Thursday (AEDT) could push more moderate Republican votes in her favour.

Announcing his decision at a town hall event in New Hampshire, Christie warned that November’s election would be “a fight for the soul of our party and the soul of our country”.

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“We need to be willing to take the responsibility for the part we’ve played in getting here,” the former New Jersey governor said.

“Our country is angry. It’s divided. It’s accomplishing little and it is leading our citizens to be exhausted.”

Other candidates in the mix are biotech entrepreneur Vivek Ramaswamy, 38, who is pitching himself as a “new generation” Republican, as well as former Arkansas Governor Asa Hutchinson and Texas pastor Ryan Binkley. All three are seen as long shots.

Could there be surprises?

Polls suggest Trump, who at least 30 points ahead of his main rivals in Iowa, has such a commanding lead that his victory is all but assured.

But polls haven’t always been accurate and the former president’s numbers are so high that there’s always a risk that it breeds complacency – particularly when snow and near-freezing conditions could affect voter turnout on the night.

Indeed, the weather in Iowa has been so punishing in recent days that Trump’s campaign had to cancel events involving surrogates for the former president. Ramaswamy’s car also got stuck in a ditch this week driving in snow from the capital of Des Moines to north-west Iowa, while Haley had to call off an event on Monday in Sioux City.

Trump has also run a very different ground game to his opponents. He hasn’t been in the state as much as his rivals, refused to show up to Republican debates and has relied on campaign rallies – where he gives a speech but takes no questions from voters – to rev up his base.

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That base makes up about 37 per cent of Republican Party members, which is about the same percentage of persuadable Republicans.

The Iowa caucus is also a secret ballot, which means Republicans do not have to show their neighbours who they are voting for. This could make a difference if there’s anti-Trump sentiment that isn’t being picked up in the polls.

He’s not expected to lose, but politics is often unpredictable – especially in America.