Donald Trump held an early lead in Iowa's first-in-the-nation Republican nominating contest on Monday, according to an Edison Research entrance poll, as Iowans braved frigid temperatures to gather at schools, community centers and other locations to formally kick off the 2024 U.S. presidential campaign.

The former president's dominant position has turned the contest into a race for second place, as both Florida Governor Ron DeSantis and former U.N. Ambassador Nikki Haley aim to emerge as the chief alternative to Trump.

The Iowa contest, known as a caucus, got under way at 7 p.m. local time on Monday (0100 GMT on Tuesday). The entrance poll results include the first people arriving at caucus sites, a group that might not be representative of all voters casting ballots on Monday.

 Opinion polls show Trump enjoys broad support from Republican voters in the Midwestern rural state, even though he faces four criminal cases that could potentially land him in prison before the Nov. 5 election.

 Edison's entrance poll also found four in 10 saying immigration was the issue that mattered most in deciding who to support on Monday and four in 10 said the economy; the rest cited foreign policy or abortion.

A commanding victory for Trump in Iowa would bolster his argument that he is the only Republican candidate capable of taking on Democratic President Joe Biden.

 I'm hoping that it's a landslide, and I wouldn't be surprised," said Kim Pitts, 65, a retired Christian bookstore owner and Trump supporter.

A big Trump victory would spell trouble for his challengers, especially DeSantis, who has wagered his campaign on the Iowa caucus, barnstorming all of its 99 counties.

 A third-place finish could prove fatal to DeSantis's prospects. Polls show him far behind Trump and Haley in the more moderate Northeastern state of New Hampshire, where Republicans will choose their nominee eight days from now.

Other contenders in the race include former biotech investor Vivek Ramaswamy, who stoked interest last year as a potential alternative to Trump but has failed to gain traction, as well as former Arkansas governor Asa Hutchinson.

 Unlike a regular election, Iowa's caucus requires voters to gather in person in small groups, where they will cast secret ballots after speeches from campaign representatives. Results are expected several hours after the caucuses start.