Donald Trump scored his second straight victory Tuesday in the race for the U.S. Republican presidential nomination, further cementing his grip on the party and raising doubts about his sole remaining rival Nikki Haley's path forward.

Despite facing a host of legal problems, including 91 criminal charges in four separate cases, the former president's win greatly increased the likelihood he will seal the nomination and head into a general election rematch in November against his successor Joe Biden.

While Haley, who served in the Trump administration as U.S. ambassador to the United Nations, is expected to face increased pressure from Republicans to pull out of the race, she said it is "far from over," calling herself a "fighter" and vowing to stay on.

Republican presidential candidate and former U.S. Ambassador to the United Nations Nikki Haley delivers remarks at her primary night rally in Concord, New Hampshire, on Jan. 23, 2024. (Getty/Kyodo)

"There are dozens of states left to go and the next one is my sweet state of South Carolina," she told supporters in New Hampshire.

Trump hit out at Haley after major U.S. media organizations predicted victory for him, saying she had had a "very bad night" and questioning why the former ambassador is still "hanging around."

Thanking his supporters, Trump said he had had a "great evening," while also lashing out at Biden and popular New Hampshire Gov. Chris Sununu, who had endorsed Haley.

Trump is the first non-incumbent Republican candidate to win the party's first two presidential contests in Iowa and New Hampshire.

The nation's first Republican primary for the upcoming election was a two-person race between Trump and Haley, who sought to gain support from independents, making up nearly 40 percent of the state's registered voters.

Republican presidential candidate Donald Trump (C) speaks at a primary election night party in Nashua in the state of New Hampshire on Jan. 23, 2024. (AP/Kyodo)

While the final margin between the two remains unclear, with more than 90 percent of the estimated votes counted before 3 a.m. on Wednesday, Trump had 54.6 percent, compared with 43.1 percent for Haley, according to The Associated Press.

The primary took place two days after Florida Gov. Ron DeSantis ended his bid for the nomination and endorsed the 77-year-old former president.

Following a third-place finish eight days ago in the Iowa caucuses, Haley, who turned 52 recently and has called for a "new generational conservative leader," was hoping to upset Trump in New Hampshire.

Unlike Iowa, where conservative evangelical Christians hold sway in politics, the small New England state, with a population of about 1.4 million, is known to have a large body of moderate Republicans, independents and highly educated voters.

Haley, also a former South Carolina governor, was counting on them and some Democrats to help her stem Trump's popularity, claiming that only she can win a general election against President Joe Biden, who is almost certain to be the Democratic nominee.

Primaries in New Hampshire are unique as they are run by the state and its rules allow independents, or so-called undeclared voters, to choose which party's contest they participate in.

However, in a departure from past practice, the Democratic National Committee made South Carolina its first official nominating contest on Feb. 3, as the party wanted to prioritize a state more racially or ethnically diverse than New Hampshire.

The change was seen as working in favor of Haley, given her strategy to attract anti-Trump votes, including from Democrats who would have written Biden's name were he on the ballot.

But even under such circumstances she was unable to win, reflecting Trump's commanding position to become the Republican's pick for president.

DeSantis, once considered Trump's top challenger, salvaged a distant second place in the Jan. 15 contest that kicked off the Republican nomination calendar. But before his withdrawal announcement on Sunday, he was polling in the single digits in New Hampshire after focusing his efforts and spending on Iowa.

A primary is akin to an ordinary election, with provisions such as allowing absentee voting, whereas a caucus resembles a community gathering that requires voters to turn out in person at a specific time and place to pick a presidential nominee.

Up for grabs in the New Hampshire primary were 22 delegate votes for the Republican Party's national convention in July. Trump's victory in Iowa has already given him 20 of the 40 delegates from the rural Midwest state.

Although the two states account for only a fraction of the total 2,429 Republican delegates nationwide, history has shown that the first contests have a huge impact on the subsequent nomination process.

In New Hampshire's largely symbolic Democratic primary, which did not award delegates, Biden easily won over two challengers thanks to a write-in campaign carried out by his supporters.

In recent days, a number of former Trump rivals have closed ranks behind him, including Tim Scott, the only black Republican in the Senate, who pulled out of the presidential race in November.

Scott's endorsement, announced Friday, has fueled speculation that he might become Trump's choice for runnig mate should the former president capture the nomination. As the influential senator is from Haley's home state of South Carolina, his decision to rally behind Trump was a particularly big blow to her.

The primary vote in South Carolina, due to take place on Feb. 24, is the next key event in the nomination calendar, and Haley is so far trailing Trump in the polls.

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