- By Francesca Gillette
- BBC News
Donald Trump faces his last Republican challenger, Nikki Haley, in Tuesday's New Hampshire primary.
The former US president hopes to deliver a knockout blow to the former South Carolina governor's campaign for the Republican nomination.
Ms. Haley hopes New Hampshire's constituency of independent voters will help her pull off an upset victory.
The race follows Trump's landslide victory in Iowa last week.
The eventual Republican nominee will challenge Democratic nominee President Joe Biden in the November general election.
The race between Mr Biden, 81, and Mr Trump, 77, will be rematched in the 2020 presidential election.
Democrats also vote in their primary in New Hampshire on Tuesday, but Mr Biden will be the first sitting president not to appear on the ballot because of a dispute between national and local party officials.
The race for the Republican nomination narrowed to two Sunday after Florida Gov. Ron DeSantis finished second in Iowa's caucuses.
Mr Trump already had a double-digit lead in several polls in New Hampshire before Mr DeSantis left. Most polls show a majority of the Florida governor's supporters view Mr Trump as the next best choice.
At a rally in Laconia, New Hampshire on Monday night, Mr Trump said: “If you want a losing candidate who will put America last, vote for Nikki Haley.”
He told the crowd that “globalists and far-left communists” were trying to convince liberals to vote for him in the Republican primary.
“They want to run against her because she's so easy to beat,” he added.
Most voters in New Hampshire will cast their ballots during the day Tuesday, but in tiny Dixville Notch, a handful of people cast ballots at midnight in a decades-old tradition. All six registered voters in the resort town chose Nikki Haley over Donald Trump.
At a campaign event earlier in the day, Ms Haley, 52, said Mr Trump was interested in the criminal and civil cases he faces. He denies all charges, claiming political persecution.
“When you hear Trump talk, what does he talk about? Grievances, the past. Retributions.
“Biden talks about investigations. Not one of them talks about the future. I'm doing this because… I don't want my kids to live like this.”
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UN Under President Trump Ms Haley, who was the ambassador, added: “When you go out on Tuesday, you're going to decide: do you want more or do you want something new?”
Anyone in New Hampshire can vote in the primary, and the state is considered more moderate than deeply conservative Iowa. Mr Trump won the state in 2016 and 2020 as the Republican candidate.
The Haley campaign is hoping for a potential shock victory over 40% of New Hampshire's independent registered voters.
Tuesday's Democratic New Hampshire primary is at the center of a dispute between state party officials and the Democratic National Committee.
New Hampshire is usually at the top of the US election calendar, but the national DNC switched the order to South Carolina, arguing that it better reflects the country's diversity.
Local party officials in New Hampshire decided to hold the primary anyway, so the DNC would not award any delegates, effectively not certifying the results, and Mr. Biden would not be on the ballot.
Instead, some of Mr Biden's Democratic allies in New Hampshire are urging voters to put his name on the ballot when they cast their ballots.