Donald Trump all but nailed down a rematch with President Joe Biden after winning the New Hampshire primary, promising 10 months of unprecedented tension and bitterness.

Trumps only remaining challenger, Nikki Haley, vowed Wednesday to fight on despite her defeat, but no Republican has ever won both opening contests and not ultimately secured the partys nomination.

A rambling Trump previewed the divisive rhetoric to come with a victory speech that attacked Haley for having a very bad night and even lashed out at her dress.

I dont get too angry, I get even, the 77-year-old said.

Biden, 81, said it was now clear that Trump would be the Republican nominee for Novembers election and warned that the future of American democracy itself rode on the result.

While polls show that most Americans dont want a contest between the two oldest presidents in US history, Bidens campaign says it is relishing another shot at the man he beat in 2020.

Donald Trump is running a campaign of revenge and retribution, Biden campaign manager Julie Chavez Rodriguez told reporters Wednesday. Joe Biden and Kamala Harris are running to move the country forward.

˜Make America Normal Again?

Haley had hoped for a major upset in New Hampshire, but Trump - her former boss when she was UN ambassador - won by around 54 percent to 43 percent.

She went on the offensive Wednesday, heading to South Carolina, where she launched attack ads targeting Trump as too much chaos as she tries to turn around weak polling in her home state ahead of its February 24 primary.

Trump is completely consumed by his own perpetual drama and grievances, Haleys communications director Nachama Soloveichik said.

Playing on Trumps beloved Make America Great Again slogan, Soloveichik said voters must choose Make America Unhinged Again or Make America Normal Again.

The twice-indicted former president has kept to his hard-right messaging, with no hint of reaching out to moderate voters who supported Haley.

At one point swearing on primetime TV late Tuesday, Trump said the United States was a failing country and loaded his speech with ominous warnings about immigration and false claims about winning the 2020 election.

He lashed again out at Birdbrain Haley on social media on Wednesday morning.

˜Struggling

Biden meanwhile cruised to victory in an unofficial Democratic primary in New Hampshire, giving him a symbolic boost.

The president is focusing on hot-button issues including abortion, as his economic message fails to resound with inflation-hit voters.

After Trumps win, he said the stakes could not be higher in the coming election.

His campaign is now selling merchandise for a rematch, including a t-shirt reading: Together, we will beat Trump. Again.

The election race isalready being watched closely around the world, with US allies Ukraine and Israel embroiled in wars, and concerns about Trumps foreign policy plans including a possible pullback from NATO.

US media said that the New Hampshire results did hold hope for Biden, despite polling showing him neck and neck or even behind Trump.

Not only did Trump lose nearly half the Republican vote, but his failure to win over independents and floating voters gave succor to Democrats.

He is struggling to make himself palatable to these key constituencies that will ultimately decide the election, Biden campaign official Quentin Fulks said. (AFP)