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A brash Gov. Chris Sununu has a message for Nikki Haley's rivals for the Republican presidential nomination - it's time to get out of the race. 

"This is a race between two people – Nikki Haley and Donald Trump. That’s it," Sununu stated as he spoke with reporters after endorsing Haley for president on Tuesday, at a town hall event at a ski lodge in New Hampshire's largest city.

Sununu, the popular Republican governor of the state that holds the first primary and second overall contest in the GOP presidential nominating calendar, emphasized that "with all due respect to all the other candidates, this is a two-person race at this point."

The endorsement will likely have little immediate impact on the former president, who remains the commanding front-runner for the GOP nomination as he makes his third straight White House run.

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Sununu endorses Haley

Republican Gov. Chris Sununu of New Hampshire (right) endorses former ambassador and former South Carolina Gov. Nikki Haley, at a campaign event in Manchester N.H. on Dec. 12, 2023  (Fox News - Paul Steinhauser)

But Sununu's much coveted backing of Haley, the former two-term South Carolina governor who later served as ambassador to the United Nations in the Trump administration, is seen as a setback for the two other Republican presidential candidates who were also in the running to land the endorsement - former New Jersey Gov. Chris Christie and Florida Gov. Ron DeSantis.

"Chris and Ron have been running great campaigns. Both are very good friends. Great governors in their own right," Sununu said in a Fox News Digital interview after endorsing Haley.

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But he added that one of the reasons he chose to endorse Haley is that "she’s really connecting on the campaign trail. Her numbers are moving."

"I’m behind Nikki Haley. I think they should all get out frankly, including former President Trump. I think everyone should kind of clear the way," Sununu said when asked about Haley's rivals. 

But he quickly acknowledged "they’re going to keep campaigning."

Nikki Haley and Governor Chris Sununu

Republican presidential candidate and former U.S. Ambassador to the United Nations Nikki Haley is endorsed by New Hampshire Governor Chris Sununu at a campaign town hall in Manchester, New Hampshire, on December 12, 2023.    (REUTERS/Brian Snyder)

Sununu's endorsement of Haley appears to be a big blow for Christie, who just as he did in his unsuccessful 2016 White House bid, is once again betting it all on New Hampshire.

Sununu told Fox News that he hadn't talked to Christie ahead of his endorsement of Haley. 

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Haley, asked by Fox News if Christie should depart the race in the wake of her landing Sununu's endorsement, said "Chris is my friend and I will never tell anyone to get out of the race. It’s a personal issue to get in. It’s a personal decision to get out. That’s Chris’ decision to make."

Sununu will join Haley for three more campaign events on Wednesday and Thursday in New Hampshire. The governor will be stumping with Haley across the Granite State as Christie returns Wednesday to New Hampshire for two events.

Christie's campaign, in a statement, emphasized that Sununu's endorsement of Haley "puts us down one vote in New Hampshire and when Governor Christie is back in Londonderry tomorrow, he’ll continue to tell the unvarnished truth about Donald Trump and earn that one missing vote and thousands more."

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As he worked to land Sununu's endorsement, Christie spotlighted that when it comes to Trump, he and the New Hampshire governor were on the same page, as two of the most vocal GOP critics of the former president.

"Who does he want standing across from Donald Trump when this gets down to a one-on-one? Who does he think can take him on in a direct way? Who’s been saying the same things as Chris Sununu has been saying for the last couple of years about Donald Trump, trying to move the party in a new direction? And I think I’m the person who has the clearest, strongest voice on that," Christie emphasized in a Fox News Digital interview a couple of weeks ago. 

Chris Christie

Former New Jersey Gov. Chris Christie (right), who's running a second time for the Republican presidential nomination, teams up with New Hampshire Gov. Chris Sununu (center) at a town hall in Nashua, N.H. on Nov. 2023. (Fox News)

Christie in recent weeks has also stepped up his criticism of Haley's much more measured jabs at Trump.

Haley, at Tuesday's event, once again repeated her well-worn line that Trump was "the right president at the right time."

Asked if Haley's more passive attacks on Trump were an issue, Sununu told Fox News "not at all."

"A candidate has to be talking about what they’re about, not just what the other guy isn’t. I think there’s always an opportunity to talk about the former president in terms of where he succeeded and where he didn’t – and there’s a lot of didn’t there. But I think Nikki’s done a great job not just talking about him but what she’s about," he argued.

And Haley emphasized to reporters that "I talk about my differences with Trump."

"Anti-Trumpers don’t think I hate him enough. Pro-Trumpers don’t think I love him enough," she added. "At the end of the day I put my truths out there and let the chips fall where they may."

Haley, who has enjoyed momentum in the polls in recent months, thanks in part to well-received performances in the first three GOP presidential primary debates, leapfrogged DeSantis for second place in New Hampshire and her home state, which holds the first southern contest. Christie stands in third place in most of the latest surveys in New Hampshire.

Haley also aims to make a fight of it in Iowa – the state whose Jan. 15 caucuses lead off the GOP nominating calendar. The latest polls suggest she is close to pulling even with DeSantis for a distant second place behind Trump.

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While Sununu's backing of Haley is also a setback for DeSantis, it likely won't sting as much as it does for Christie.

DeSantis is mostly concentrating on Iowa, where he enjoys the endorsement of Republican Gov. Kim Reynolds. He's also backed by Bob Vander Plaats, president of The Family Leader, a top social conservative organization in a state where evangelical voters play an outsized role in Republican politics.

Ron DeSantis teams up with Chris Sununu in New Hampshire

Florida Gov Ron DeSantis (left), a 2024 Republican presidential candidate, teams up briefly with GOP Gov. Chris Sununu of New Hampshire, on August 19, 2023 in Londonderry, N.H.  (Fox News - Paul Steinhauser)

DeSantis, who is spending most of his time in Iowa, is expected back in New Hampshire on Friday.

"What happens in New Hampshire will be significantly impacted by the outcome in Iowa, where the true Trump alternative will emerge. And when Ron DeSantis comes out in that position, he will be joined by over 60 New Hampshire state legislators who stand ready to take the fight to the establishment and their candidates of yesteryear to return power to grassroots conservatives," DeSantis campaign spokesman Andrew Romeo argued in a statement.

And at a town hall in Iowa hosted by CNN, DeSantis on Tuesday evening argued that "even a campaigner as good as Chris Sununu is not going to be able to paper over Nikki Haley being an establishment candidate."

Get the latest updates from the 2024 campaign trail, exclusive interviews and more at our Fox News Digital election hub.