The New Hampshire Republican primary has effectively boiled down to a two-person race between former President Donald Trump and former U.N. Ambassador Nikki Haley, political experts told Boston Public Radio on Friday.

Trump hasn't had to put much time on the ground in the Granite State because he already has an established base of voters. Haley, meanwhile, has been dropping by diners and retail stores in her appeal ahead of the primary — and she's found support from non-Republicans.

In New Hampshire, voters who are registered as undeclared can opt for either the Democratic or Republican ballot once they arrive at the polls. And it's not a small group: More New Hampshire voters are undeclared than those registered as Democrats or Republicans. The question is: How great an impact will those voters have on Tuesday?

"Can she muscle through on the backs of Independent or undeclared voters who want to turn the page, want their vote to be a vote against Trump?" CBS News national correspondent Caitlin Huey-Burns said on Boston Public Radio.

Haley's campaign is getting some outside help. The political action committee PrimaryPivot is targeting those undeclared voters, urging them to vote in the state's Republican primary.

"If people want to actually vote against Trump, rather than try to embarrass our president [by voting in the Democratic primary for another candidate] they should vote in the Republican primary against Trump," said PrimaryPivot co-founder Robert Schwartz.

Multiple voters called and texted Boston Public Radio to say they plan to do just that: Vote for Haley to "take away a vote" from Trump, then cast their ballots for President Joe Biden in the general election.

It's not an unusual strategy getting Independents and voters from an opposing party to support an alternative candidate. But whether these voters can make a big enough difference to result in a Haley win on Tuesday "totally depends on the turnout," Schwartz said.

Former New Hampshire GOP Chair Jennifer Horn doesn't think it's likely. She pointed to polling that shows Trump has remained the favorite even as Haley's popularity has increased.

"There's a part of me that feels sorry for all those voters out there who are looking at her as our last best chance to defeat Trump," she said.

Horn said Haley has not made a strong enough case against Trump to sway voters who would cast their ballots for him.

"In New Hampshire, even though there are more moderate Republicans and you think they'd kind of go for her because she has this traditional Republican experience and vision of the world, they're still pretty all-in for Donald Trump," Horn said.

Watch Boston Public Radio from Manchester, New Hampshire