With Trump's victory seemingly a foregone conclusion before Monday given his sizable lead in opinion polls, the intrigue centred on the race for second place between Florida Governor Ron DeSantis and former United Nations Ambassador Nikki Haley. The two candidates have waged an increasingly bitter battle to emerge as the chief alternative to Trump.
Iowans braved life-threatening temperatures on Monday to gather at more than 1600 schools, community centres and other sites for the state's first-in-the-nation caucus, as the 2024 presidential campaign officially got under way after months of debates, rallies and advertisements.
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, despite the four criminal cases Trump faces that could potentially turn him into a convicted felon before the November general election.
Both DeSantis and Haley were aiming for a strong second-place finish that could demonstrate they might prevent Trump's inexorable march toward the nomination.
DeSantis in particular had wagered his campaign on Iowa, barnstorming all of its 99 counties, and a third-place finish could increase pressure to end his bid.
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.
Unlike a regular election, Iowa's caucus requires voters to gather in person in small groups, where they cast secret ballots after speeches from campaign representatives.
The wind chill in parts of the state had been forecast to reach minus 43C on Monday, according to the National Weather Service, potentially depressing turnout.
If so, Trump's grip on his most loyal supporters may have given him an edge.
DeSantis and Haley had expressed confidence they would exceed expectations in Iowa, though neither predicted victory.
"If you're willing to brave the cold and turn out for me, I'll be fighting for you for the next eight years, and we're going to turn this country around," DeSantis told a crowd earlier in the day in Sergeant Bluff.
Entrepreneur Vivek Ramaswamy, who has praised Trump, and former Arkansas Governor Asa Hutchinson, who has criticised Trump, were also running in Iowa, though neither was expected to garner much support.
Unlike his rivals, Trump did not attend many campaign events, relying instead on others to rally his supporters.
