DES MOINES (AFP)

Donald Trump stormed towards New Hampshire on Tuesday, knowing that a repeat of his runaway win in Iowa would all but seal the Republican nomination to set up his rematch with President Joe Biden in November.

The scandal-plagued former president romped home in the first contest of the drawn-out US presidential race, scoring 51 percent of Republican voters to trounce rivals Ron DeSantis and Nikki Haley for the biggest Iowa caucuses victory in modern history.

In a sign of the unprecedentedly turbulent times ahead, Trump's first stop on Tuesday was in New York for a civil defamation trial.

The three Republican contenders will then all meet for the next contest in the New Hampshire primary next Tuesday and Trump, 77, will have a chance effectively to deliver a killer blow.

"I really think this is time now for everybody, the country, to come together," Trump told a victory rally in Iowa in an unusually conciliatory tone.

However the tycoon and former reality TV star then quickly pivoted to his usual harsh rhetoric, promising to shut the Mexican border to stop an "invasion" of migrants and pledging to drill for oil if reelected.

Trump's abrasive message has divided the country as he seeks what he says will be retribution against Biden, who beat him in 2020 in a result that Trump refused to accept.

Yet it's also a message that has delivered Trump a powerful base of support.

"Trump is demonstrating impressive strength among blue-collar, working-class and rural voters. His victory was not a surprise," Dennis J. Goldford, a political science professor at Drake University in Des Moines, told AFP. 

'Night for victory'

Trump will hold a campaign event in New Hampshire on Tuesday night -- after appearing in court in New York where he is on trial for defamation in the wake of a jury finding he was liable for a 1990s sexual assault against writer E. Jean Carroll.

In blizzard-battered Iowa, Trump opened an unprecedented 30-point gap over Florida Governor DeSantis, who had pinned his hopes on a strong showing in the midwestern state. Former UN ambassador Haley took third place with 19 percent.

Heart doctor Allan Latcham, 62, who voted before heading to Trump's election party in Des Moines, hailed a "night for victory."

Trump's bid for a sensational return to the White House could also benefit from a continued battle between DeSantis and Haley that avoids a single challenger to unite the anti-Trump vote.

Despite her disappointing Iowa finish, Haley, the only woman in the Republican contest, said on Tuesday she would not join the next Republican debate unless Trump is on stage too.

Trump has so far refused to take part in any debates and is unlikely to rise to the challenge from Haley in her preferred battleground of New Hampshire.

'Straighten out the world'

DeSantis is also heading to New Hampshire after a quick stop in South Carolina, seeking to deal an early blow to Haley who was formerly governor there.

But while DeSantis confirmed that he would stay in the race to "reverse the madness," he is considered weak in New Hampshire and many analysts were declaring his campaign all but dead.

Iowa meanwhile narrowed the Republican field, with biotech entrepreneur Vivek Ramaswamy dropping out and endorsing Trump. Long-shot former Arkansas governor Asa Hutchinson also ended his campaign, US media reported.

Democrat Biden is neck and neck or trailing Trump in recent polls.

Against a backdrop of US flags, Trump told his Des Moines rally on Monday that "it would be so nice if we could come together and straighten out the world."

Belgium's Prime Minister Alexander De Croo, whose country holds the EU's presidency, on Tuesday urged Europe not to "fear" a Trump return and to become more self-reliant.