A win in Iowa's Republican caucuses does not guarantee a candidate will go on to be their party's presidential candidate.

In fact, it’s often off the mark.

Let’s take a look at the past few Republican winners.

• 2020 - as incumbent, Donald Trump's path was pretty clear and he won both Iowa and the presidential nomination
• 2016 - Ted Cruz won Iowa, but Trump won the presidential nomination
• 2012 - Rick Santorum won Iowa, Mitt Romney won the nomination
• 2008 - Mike Huckabee won Iowa, John McCain won the nomination
• 2004 - there was no Republican caucus, as George W Bush faced no challenger
• 2000 - SPOT ON! George W Bush won both Iowa and the nomination

Bernd Debusmann Jr
Reporting from Des Moines

Image source, Getty Images

I just ducked into my hotel lobby for a quick coffee and a respite from the biting cold - and bumped into Tom Gioia, a university friend of Ron DeSantis from Yale.

Gioia, a native of Atlanta, Georgia, met the Florida Governor when the two were 18-year-old undergraduates - and has been involved in volunteering and fundraising for DeSantis since the campaign kicked off in May.

“I’ve been out knocking on doors and making phone calls from the campaign headquarters,” he tells me. “We’re going to head over there in a little bit and keep going.”

Like other DeSantis volunteers I’ve met, Gioia expresses confidence that the campaign’s strong “ground game” will mean that he pulls ahead tonight, despite recent polls showing him trailing Nikki Haley.

“We’re very optimistic. I think he’s gonna do very well. The guy has done everything that he can do to make the case here to Iowans,” he says. “He’s put in the work and knocked on the doors.”

Asked about the weather, Gioia says he isn't sure what will happen tonight as far as turnout - but noted that the candidates with “the most enthusiastic supporters” will be the ones with stronger results.

“I’m sure these people are used to cold weather. But I don’t know that anyone is used to the weather being this cold… but the governor has a very, very enthusiastic base. I’m looking forward to doing my part.”

What is a caucus? A caucus is a way to nominate the presidential candidate of a political party, which requires party members to attend a location in person - such as schools and churches - at a specific time. Representatives for the candidates make speeches before those present cast their votes by writing down a name.

How do caucuses differ from primaries? Most states run primary contests to nominate a presidential candidates. Primaries are less complicated, a kind of mini-election where voters cast their ballots privately, either in person or by post, over the course of polling day. Primaries are either open (meaning anyone can vote) or closed (only people registered with the party can vote).

Why is the Iowa caucus so important? Candidates care about the Iowa caucus because a positive result can provide an early boost – and thus funding – to their campaign.

But even if the caucus can provide an advantage to winners, Iowa is not a great predictor of who will be the party's nominee. Over the last 20 years, only Donald Trump in 2020 and George W Bush in 2000 won both the Iowa caucus and the party's nomination. More here.

Mike Wendling
Reporting from Davenport

Hello from Davenport, a city of about 100,000 people perched on a long bend in the Mississippi River.

There are caucus locations dotted all around the area, and later I’ll be going to the city's Central High School to see the process play out.

This has been friendly territory for Donald Trump, and the history of the area gives us some clues as to why.

Davenport was booming in the middle of last century, home to manufacturing businesses and railroad traffic. But many of those jobs went elsewhere. In many ways Davenport and other Iowa cities and towns along the Mississippi are part of the Rust Belt – the post-industrial Midwest.

Trump's message resonated in cities like this because he promised to fight trade wars on behalf of places like Davenport. That’s one reason he won in most Iowa counties along the Mississippi in the 2016 caucus, despite losing narrowly state-wide.

His campaign will be hoping for a big victory across this region tonight.

This is the first real test of Donald Trump’s front-runner status.

The latest Iowa polls from local outlet the Des Moines Register shows the former president with a 28 point lead, so can any other Republican candidate perform well enough to challenge him?

A poor showing in Iowa could lead to someone dropping out of the race entirely.

But a strong performance - even if it is not first-place - could give a shot of adrenaline to a stuttering campaign.

If any Republican voters (and big political donors) are looking for an option outside of Trump, Iowa could show us who that might be.

But it’s important to note that whatever happens today may not represent how the rest of the US is feeling.

Iowa is a largely white and rural population. And not all Republicans will caucus, so those that do turn up in the below-freezing conditions may not represent any broader trend.

Kayla Epstein
Senior reporter

Image source, Reuters

Donald Trump is giving new meaning to the term "die-hard fan."

At a rally in Indianola, Iowa last night, he told his supporters to go to extremes to vote for him.

“You can’t sit home,” Trump said. "If you’re sick as a dog, you say 'darling, I gotta make it'. Even if you vote and then pass away, it’s worth it."

This is generally not advice any medical professional would give.

But Trump wants his supporters fired up to deliver him a massive margin of victory. The Republican caucuses require voters to attend in-person. If you don't show up, you don't get to vote.

With temperatures plunging to historic lows, there's a great deal of fretting about turnout tonight and who it might affect.

Bernd Debusmann Jr
Reporting from Des Moines

Image source, Getty Images

I’ve been in Iowa for seven days now - and it’s been cold. Very cold.

We saw heavy snow begin to accumulate on Thursday night across the state, followed on Friday by plummeting temperatures and ferocious winds.

Even just a few minutes outside has been unpleasant - fingers freeze and exposed skin stings. On Thursday, it felt as if my eyelids briefly froze shut as I stood outside to film something.

Late last week, the conditions prompted the local office of the National Weather Service and local authorities to warn of life-threatening conditions that could lead to frostbite in just 10 minutes, and cause whiteout conditions on roads.

This prompted some analysts and Iowans to speculate that turnout for the events may be lower than anticipated. The candidates themselves have also pleaded with supporters to make sure they turn out. But Iowans we’ve spoken to have, for the most part, been stoic about the weather.

“There’s so much at stake,” Iowa resident Mike Powers said on the sidelines on a Ron DeSantis campaign event at a barbecue restaurant in the Des Moines suburbs of Ames."Iowans take this pretty seriously, being a first-in-the nation caucus."

Another Iowan, Bruce Jarvis, put it more simply. "People think it’s a responsibility,” he said. “If they care about politics, they’ll be going.”

Kayla Epstein
Senior reporter

Victory looks different for the three top performing candidates in Iowa. If your name isn't Donald Trump you don't need to win today - but you better do well.

“The other campaigns want to say this is the opening bout of a heavyweight fight," Jimmy Centers, a long-time Iowa Republican consultant tells me. "Donald Trump wants this to be the knockout punch.”

Donald Trump: He needs huge victory to establish a sense of inevitability and strength. He's acknowledged this openly to supporters.

"The poll numbers are scary because we're leading by so much," he said at a 19 December rally. "If we win in a massive number, but it's a little bit less than that, they'll say, 'Oh, he didn't meet expectations.'"

Nikki Haley: Haley is experiencing a late surge of momentum after languishing in the polls for much of last year. A very strong third-place showing will demonstrate that momentum was real, Iowa operatives told me.

In a best-case scenario, she sneaks into second place, establishing herself as a real contender against Trump.

Ron DeSantis: The stakes are highest for him right now. His campaign poured everything into Iowa, but a new Iowa poll shows Trump with a huge lead.

He needs to come in second, several Iowa politicos told me, or it's not looking good.

Nomia Iqbal
North America Correspondent in Des Moines

The advice by officials is don’t stay out in the cold for more than 10 minutes.

Naturally, last night our team decided a nice downtown bar is the ticket. There we find 25-year-old Nate Cowen who is here with his fiancée. She doesn't do politics, but he does - however he hasn’t decided if he will caucus.

"I’m not a huge fan of anyone [who is] running. I feel like not a lot is being done to represent working class people."

How does he feel about the projection that Trump is likely to win Iowa?

"I just think quite frankly, with what’s going on in our nation, Trump is not really the best to represent us. I think we need someone potentially new and younger to push us through the 21st Century."

Will the cold put him off going out?

"It’s definitely going to play a part for some people because the roads are not good. People may be dissuaded from driving. Me, personally, I’m downtown so a lot of polling stations are pretty close for me. We’ll see."

Factors besides politics might affect voter turnout in Iowa - with Ames, north of Iowa capital Des Moines, waking up to -24C (-11F) this morning.

The icy weather is set to continue throughout the day with highs of -19C.

Image source, EPA

Iowa is the first major state-wide vote to determine a Republican US presidential candidate for the 2024 election.

This is where we health-check the political campaigns of those vying to win the White House.

Think of it as the official start of a months-long race for the Republican nomination, with the winner to take on the likely Democrat nominee - US President Joe Biden..

How it works is the Republican party holds a whole lot of meetings across Iowa which are called caucuses. These start at 19:00 local time (20.00 ET/01.00 GMT).

Surrogates for the Republican candidates will attend and make their final pitch, then the caucus-goers vote on their preferred candidate.

Results from each caucus are then sent to the party to tally up.

The focus today is on Republicans because Iowa Democrats will cast their votes by mail, with the mail results to be announced on 5 March. Biden is the presumptive Democrat nominee.

Brandon Livesay
Reporting from Des Moines, Iowa

Well, the race has been going on for pretty much all of 2023 - but you can think of the Iowa caucuses as the start of the 2024 election cycle.

It’s blisteringly cold here in Des Moines, the capital city of Iowa. It’s been so freezing (we’re talking a wind chill of -40C/F) that a whole stack of campaign events planned over the weekend were cancelled or turned into online streams.

Iowans are used to snow, but I’ve been chatting with locals who say this isn’t normal - this is some next-level winter weather.

It could possibly stop some folk venturing out to the caucuses - which are the meetings where votes are cast.

It’s just the Iowa Republicans who will caucus for who they want to be their 2024 candidate today, Democrats cast their votes by mail and have until 5 March to do so.

Donald Trump holds a commanding lead in the latest polls. And whatever happens today could boost or break the campaigns of the former president’s key rivals - Nikki Haley and Ron DeSantis.