Florida governor Ron DeSantis finished well behind in second place, Edison Research projected, edging out former UN Ambassador Nikki Haley as they battle to emerge as the chief alternative to Trump.

Trump was poised to win by an unprecedented margin for an Iowa Republican contest, strengthening his case that his nomination is a foregone conclusion given his massive lead in national polls even though he faces four criminal indictments.

“THANK YOU IOWA, I LOVE YOU ALL!!!” Trump wrote on his social media platform Truth Social on Monday.

With nearly 90 per cent of the expected vote tallied, Trump had 50.9 per cent, while DeSantis was at 21.4 per cent and Haley 19.0 per cent, according to Edison. The largest margin of victory for an Iowa Republican caucus had been 12.8 percentage points for Bob Dole in 1988.

Entrepreneur Vivek Ramaswamy ended his long-shot presidential bid after earning just under 8 per cent of the vote on Monday and endorsed Trump in a speech to supporters.

It was too early to say whether Trump would exceed 50 per cent, a psychological figure that would further weaken his rivals’ argument that his march to the nomination can be derailed.

Both DeSantis and Haley had been aiming for a strong second-place finish to convince donors and supporters that their challenges to Trump remain viable.

DeSantis in particular had wagered his campaign on Iowa, barnstorming all of its 99 counties and pouring resources into the state.

The result on Monday will undoubtedly keep both DeSantis and Haley in the race, ensuring Trump’s opposition remains fractured as the campaign moves to other states.”We’ve got our ticket punched out of Iowa!” DeSantis told supporters in West Des Moines on Monday.

Republicans in more moderate New Hampshire will choose their nominee eight days from now. Polls show Trump with a smaller lead over Haley there, with DeSantis far behind.

Caucus-goers appeared broadly supportive of Trump, according to an Edison Research entrance poll.

Only one-third of caucus-goers said Trump would be unfit for president if convicted of a crime. Nearly two-thirds said they did not believe Biden legitimately won the 2020 election, embracing Trump’s falsehoods about voter fraud.

“Trump is very narcissistic, he’s very cocky, but he’s going to get stuff done,” said Rita Stone, 53, a Trump backer, who attended a caucus at a West Des Moines high school.

Like many other voters, Stone said her leading concern was the US southern border with Mexico, praising Trump’s effort to build a wall when he was president.

Trump has aimed to create an air of inevitability around his campaign, skipping all five of the Republican debates thus far and largely eschewing the county-by-county politicking that most candidates do ahead of the Iowa vote.

Iowa has historically played an outsized role in presidential campaigns due to its early spot on the campaign calendar.

But the winner of Iowa’s Republican caucuses did not go on to secure the nomination in the last three competitive contests in 2008, 2012 and 2016.

A political battleground that backed Democrat Barack Obama in 2008 and 2012, the state is now seen as reliably Republican in presidential elections as registered Republicans edge out Democrats.