By Gram Slattery, James Oliphant and Nathan Layne

MANCHESTER, New Hampshire (Reuters) -Donald Trump won New Hampshire's Republican presidential primary election on Tuesday, Edison Research projected, moving closer to a likely November rematch with Democratic President Joe Biden even as his only remaining rival, former U.N. Ambassador Nikki Haley, vowed to soldier on.

"This race is far from over," she told her supporters at a primary night party in Concord, challenging Trump to debate her. "I'm a fighter. And I'm scrappy. And now we're the last one standing next to Donald Trump."

With 25% of the expected vote tallied, according to Edison, Trump had 55.0% compared with 43.5% for Haley, who had hoped the Northeastern state's sizable cadre of independent voters would carry her to an upset win that might loosen Trump's iron grip on the Republican Party.

Instead, Trump will become the first Republican to sweep competitive votes in both Iowa - where he won by a record-setting margin eight days ago - and New Hampshire since 1976, when the two states cemented their status as the first nominating contests.

While the final margin was still unclear, the results will likely increase calls from some Republicans for Haley to drop out of the race, though her campaign vowed in a memo on Tuesday to push forward until "Super Tuesday" in early March, when Republicans in 15 states and one territory vote on the same day.

Trump took to the Truth Social app to let loose against Haley. “DELUSIONAL!!!” he posted. A minute later, he added, in reference to Iowa: “SHE CAME IN THIRD LAST WEEK!”

The next competitive contest is scheduled for Feb. 24 in South Carolina, where Haley was born and served two terms as governor. Despite her ties, however, Trump has racked up endorsements from most of the state's Republican figures, and opinion polls show him with a wide lead.

Haley finished third in Iowa, just behind Florida Governor Ron DeSantis, while focusing much of her early campaign on New Hampshire, where the more moderate electorate was expected to offer perhaps her best chance of winning a state over Trump.

DeSantis, once seen as Trump's most formidable challenger, dropped out on Sunday and endorsed Trump.

Meanwhile, Edison projected Biden would win the New Hampshire Democratic primary based on write-in votes, after he declined to appear on the ballot due to a dispute with the state about the election's timing.

Despite Trump's win on Tuesday, exit polls hinted at his potential vulnerabilities in a general election campaign. He faces four sets of criminal charges for a range of offenses, including his efforts to overturn his 2020 defeat and his retention of classified documents after leaving the White House in 2021.

About 44% of voters who participated in the Republican primary said he would not be fit to serve if convicted in court, according to exit polling by Edison.

More than half said they do not believe Biden legitimately won the 2020 election, echoing Trump's false claims that the result was tainted by fraud.

There were also warning signs for Biden, however. Nearly three-quarters of Republican primary voters said the economy was either poor or not good, an area where Biden has struggled to highlight his administration's accomplishments.

Republicans made up a smaller share of voters in the primary relative to the state's 2016 Republican contest in the state, the exit polls showed. Some 49% of voters considered themselves Republican, compared to 55% in the 2016 primary. Six percent said they considered themselves Democrats, compared to 3% in 2016. The share of independents was little changed at 45%.

BIDEN NOT ON BALLOT

Biden was not on the ballot in New Hampshire's Democratic primary, having supported an effort by his party to move their first primary election to the more diverse state of South Carolina.

New Hampshire supporters were still able to vote for him by writing Biden's name on the ballot, offering a barometer of his political strength. With 5% of the estimated vote counted, according to Edison, Biden had 68.3%, far ahead of U.S. Representative Dean Phillips at 19.6%.

The Democratic president, whose advisers are anticipating a rematch with Trump, took aim at Republicans over their efforts curb abortion rights in a Virginia speech on Tuesday, but his remarks were interrupted repeatedly by hecklers protesting his policies toward Israel.

The U.S. Supreme Court, with a conservative majority made possible by three justices who joined the court under Trump, eliminated a nationwide right to abortion in 2022, galvanizing Democratic voters in that year's congressional elections.

Biden also has cast Trump as a would-be dictator and a threat to democracy.

'I'M VERY CONFIDENT,' TRUMP SAYS

Trump, who is balancing campaign stops with appearances in various criminal and civil courts, denies wrongdoing and has used the criminal charges against him to bolster his claim of political persecution.

He predicted victory in New Hampshire early on Tuesday, saying the level of enthusiasm was incredible. Later, during a stop at a polling station in Londonderry, Trump briefly addressed supporters.

"So excited. I'm very confident," he said.

New Hampshire, while also a mostly white state with a small population like Iowa, has a more moderate Republican electorate and a better record of predicting the eventual nominee.

Haley had stepped up her attacks on Trump as the election drew near, criticizing his affinity for strongmen such as Russia's Vladimir Putin and North Korea's Kim Jong Un.

Haley, 52, has also gone after Trump's age - he is 77 - and mental acuity, attacks she has also regularly leveled at Biden, who is 81.

She took up the theme again on Tuesday, saying the country needs to put someone in the White House that can put in eight years to get it back on track.

"Do you want two 80-year-olds running for president?" Haley asked.