Donald Trump has defeated Indian-American politician Nikki Haley in the New Hampshire Republican primary, continuing his march toward the party's presidential nomination and a possible final contest with President Joe Biden in the November 5 election.
With three-quarters of the votes counted, Trump, 77, was leading 55 per cent to 44 per cent.
Although only two states have voted so far, Trump's victory in Tuesday's primary underscored his dominance of the Republican Party.
The former president won a landslide in Iowa's caucuses last week.
Trump's victory is remarkable, considering he faces 91 criminal charges, including those related to seeking to overturn the 2020 presidential election.
But Haley, 52, the former South Carolina governor and ambassador to the United Nations, vowed to fight on, giving a feisty speech to supporters on Tuesday night in which she questioned the former president's mental fitness and warned Republicans that renominating Trump would lead the party to defeat.
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Speaking after the results, Haley - who campaigned hard in the state - congratulated Trump, saying he "earned it". But she said the race was "far from over" with "dozens of states left to go". "I'm a fighter, and I'm scrappy," Haley, Trump's last remaining rival in the Republican nomination race, said.
Haley said when she started, there were 14 of them in the race, and she was polling at two per cent in the polls.
"And now we're the last one standing next to Donald Trump, Haley said.
A Trump nomination is a Biden win and a Kamala Harris presidency, she said.
"And the next one is my sweet state of South Carolina," she said.
Haley is hoping a strong showing in South Carolina could propel her into the March 5 Super Tuesday contests.
Trump said that Haley "had a very bad night" and was "doing a speech like she'd won" when she lost.
Trump called her "delusional".
"Who the hell was that imposter that went up on that stage that went before and claimed victory?" he asked.
Team Haley hit back almost immediately, describing his speech as a "furious and rumbling rant".
Notably, Trump is the first non-incumbent Republican presidential candidate to win both the Iowa Caucus and the New Hampshire primary back-to-back.
Trump is the only Republican candidate to have won the New Hampshire primary thrice.
This is a decisive win for Donald Trump tonight, former Republican presidential candidate Vivek Ramaswamy told Fox News in an interview. He said that Haley must withdraw from the race in favour of Trump.
In a statement, the Trump campaign asked Haley to drop out of the race.
Haley does not have a path to victory. Instead, if Haley stays in the race, she will play an active role in advancing the re-election of Harris-Biden, it said.
Nikki Haley said she's running to stop the re-election of Harris-Biden. Yet, without a viable path to victory, every day she stays in this race is another day she delivers to the Harris-Biden campaign, said Taylor Budowich, CEO of Make America Great Again Inc.
It's time for unity, it's time to take the fight to the Democrats, and for Nikki Haley: it's time to drop out, Budowich said.
On the Democratic side, President Biden, 81, won easily, even though his name did not appear on the ballot because the party had decided to bypass New Hampshire and start its primaries next month in South Carolina.
In a statement, Biden's campaign indicated that its attention was now focused on Trump, dismissing Haley's prospects as a Republican contender in the general election.
Tonight's results confirm Donald Trump has all but locked up the GOP nomination, and the election-denying, anti-freedom MAGA movement has completed its takeover of the Republican Party, the statement said.
Make America Great Again or MAGA is an American political slogan and movement popularised by Trump during his successful 2016 presidential campaign and is used to refer to his political base.
"While we work toward November 2024, one thing is increasingly clear today: Donald Trump is headed straight into a general election matchup where he'll face the only person to have ever beaten him at the ballot box: Joe Biden, she said.