- Gareth Evans & Holly Honderich & Bernd Debusman Jr
- BBC News, Des Moines, Iowa
Donald Trump and his Republican rivals are making last-ditch pitches for support in Iowa, hours before the state's voters begin the 2024 race for the White House.
Candidates are holding final events, but harsh conditions have complicated the last days of the campaign.
A landslide victory in Iowa would cement Mr Trump's lead.
His rivals, meanwhile, are seeking to position themselves as the main alternative to the former president.
Republican voters will meet at one of more than 1,500 caucus locations around the Midwest on Monday night to choose their preferred presidential candidate. With temperatures forecast to drop to -30C (-20F), all candidates have urged voters to brave the bitter cold so they can have their say in the race amid fears the weather could harm polling.
The race will move state by state before a final candidate is chosen to challenge Joe Biden in November's general election.
Iowa has a patchy record of ultimately electing a Republican nominee, and hasn't done so since 2000, when the state's voters backed George W. Bush.
Mr Trump held a rally in Indianola on Sunday and invited his supporters to attend. “We are going to make history together but you have to show up,” he said. “The outcome of this state will send a message to the entire country, indeed the entire world.”
The former president, 77, is looking to knock out his rivals and is winning by a wide margin. “We are looking to set records,” he said during a virtual rally on Friday.
His campaign has relied heavily on its ground game, with regular “commit to caucus” events serving as test runs for the real deal on Monday. The events, where “caucus captains” knock on doors and recruit Iowans, include an animated video on how to caucus, a sign of how Mr. Trump hopes to rally first-time voters and win big.
The Trump campaign's ambitions for a landslide victory showed him with a nearly 30-point lead in the final Des Moines Register/NBC News/Mediacom poll on Saturday evening.
Nikki Haley, the former US ambassador to the UN, has moved into second place after gaining momentum in recent days, a closely watched poll showed.
Florida Gov. Ron DeSantis, who has invested the most resources in Iowa, was relegated to third place. If Mr DeSantis performs badly on Monday, he will face pressure to quit and the outcome could prove crucial to his campaign.
Ms Haley, 51, quickly sought to downplay the results, saying the “real vote” was on caucus day. “We want to come out of Iowa strong,” he said.
A strong result in the state would give the Haley campaign important momentum heading into the next contest in New Hampshire, where she is polling within 10 points of Mr Trump. After that, the next race is in his home state of South Carolina, where he served two terms as governor.
A win in one of these primary states would help establish Ms. Haley as the only viable alternative to the former president, spurring much-needed support and donations.
In the final race around Iowa, Ms Haley doubled down on her pitch for change, urging voters to let go of Mr Trump's “confusion”. “It comes down to a choice,” he told supporters in Cedar Falls. “You have the opportunity to look back on the past and move on, or to move forward and start anew.”
Facing tough competition for second place, Mr DeSantis has taken an aggressive approach, attacking both Ms Haley and Mr Trump in the final days of the campaign. “Donald Trump runs on his issues. Nikki Haley runs on her donors' issues,” he often says at the start of his events. “I run for your problems.”
Mr DeSantis has kept a busy schedule of events, which he and campaign staff are quick to point out have happened despite other candidates canceling appearances due to the winter storm. He toured all 99 counties and spent considerable time in Iowa in recent weeks, focusing on organizing an effective grassroots campaign.
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The Florida governor has repeatedly questioned the accuracy of polls showing him in third place. “I think it's going to be very difficult to get a vote in the Iowa caucus,” he said during an interview with CNN on Sunday.  Polling is not accurate and predictable, but especially one at -20 degrees.”
“I know the media is saying this [Trump] Unstoppable,” he said. “At the end of the day, the people can make up their minds… there are a lot of voters who don't make up their mind.”
Elsewhere, in the east of the state, Vivek Ramasamy held an event in front of dozens of people on Sunday. The biotech entrepreneur, 38, is polling in fourth place and has become increasingly vocal about conspiracy theories in recent weeks, particularly airing false claims of election fraud in 2020.
He supported Mr Trump at the event, who attacked him publicly for the first time on Saturday, and blamed his advisers for Mr Trump's comments. He also said he was experiencing a “late surge” in support.
“This is a 'proof' moment for all the other candidates,” Jimmy Centers, an Iowa Republican consultant, told the BBC. “You say the Republican Party is better suited to go the other way, and now the voters will have their say.”