With five days to go until the primary in the key battleground state of New Hampshire, former President Donald Trump remains neutral in the last competitive and high-profile GOP Senate nomination race this cycle.

But on Thursday, Republican Gov. Chris Sununu weighed into the primary, backing one of the front-runners in the showdown — New Hampshire state Senate President Chuck Morse.

"We Republicans here in New Hampshire, we have a very big decision to make, and we have to get it right. We will be nominating New Hampshire’s next United States Senator. And for the sake of this great state, we have to defeat Maggie Hassan in November and the best candidate to do that is Chuck Morse," Sununu said as he stood next to Morse at a news conference at the governor’s mansion in New Hampshire’s capital city.

Morse is one of the co-front-runners in the crowded field of contenders, but trails retired Army Gen. Don Bolduc by double digits in the two most recent public opinion polls. The other major contenders in the multi-candidate field — cryptocurrency entrepreneur Bruce Fenton; businessman, economist and author Vikram Mansharamani; and former Londonderry, New Hampshire, town manager Kevin Smith — registered in the single digits in the surveys, and a high percentage of respondents were still undecided.

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The winner of the Sept. 13 primary will face off in November with former governor and first-term Democratic Sen. Maggie Hassan in the key general election battleground state in a race that is among a handful across the country that may determine if the GOP wins back the Senate majority. Republicans have heavily targeted Hassan, who they view as very vulnerable due to her lackluster poll numbers.

"Chuck Morse has been there every step of the way in our record of success here in New Hampshire," Sununu, who remains very popular among Granite State Republicans, said of the small business owner who’s served as president of the state senate for most of the past decade. "I couldn’t be more proud to endorse a partner that I’ve had at the Statehouse."

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Morse, in thanking Sununu for his support, emphasized that "everything that the governor and I have accomplished in the state of New Hampshire since he came in — in 2016 — is definitely driving what this state stands for."

Trump, who remains the most popular and influential politician in the GOP as he continues to play a kingmaker’s role in party politics and repeatedly teases a 2024 presidential runs, said last week that he was seriously considering endorsing one of the two polling front-runners in the race.

"I'm looking at that race very closely," Trump said on conservative radio host John Fredericks' radio program, which is popular with conservatives across the country.

Trump — who gave a big shout-out to Bolduc a year ago after the retired general during an interview on "Fox and Friends" was highly critical of President Biden's pullout of U.S. forces from Afghanistan — said in last weeks’ interview that Bolduc has "said some great things, strong guy, tough guy. I think he's doing very well, too. I hear he's up, he's up quite a bit."

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Bolduc, who served 10 tours of duty in the war in Afghanistan, is making his second straight run for the GOP Senate nomination in New Hampshire. His 2020 bid was unsuccessful, in part because Trump endorsed Bolduc's rival. After keeping Trump at arm's length in his first Senate campaign, Bolduc has strongly embraced the former president's unproven claims that the 2020 election was "rigged" and "stolen." Bolduc was part of a group of retired generals who signed a letter questioning the legitimacy of the election due to what they charged was "a tremendous amount of fraud."

While Bolduc has given New Hampshire conservatives plenty of red meat, there are concerns from some Republicans in the state and nationally that a primary victory by the retired general, who has severely struggled with fundraising, will allow Hassan to win re-election.

Last week a newly formed super PAC named the White Mountain PAC, which has loose links to longtime Senate Republican Leader Mitch McConnell's political orbit, launched a TV commercial in New Hampshire boosting Morse, as part of what the national ad tracking firm AdImpact reports is a massive $4 million reservation for airtime ahead of the primary. The group’s second ad, which launched earlier this week, targeted Bolduc.

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While Trump has remained neutral in the primary battle, former Trump White House chief strategist and former media executive Steve Bannon has heavily promoted Bolduc on his radio program. But longtime New Hampshire resident and veteran Trump political adviser Corey Lewandowski, who managed Trump’s 2016 presidential primary campaign, has heavily criticized Bolduc.

Sununu told Fox News at Thursday’s event that during the call he received last week from Trump, "I very strongly encouraged him to get involved in the race. I told him that I thought Chuck Morse wasn’t just a great candidate, but the candidate." 

Sununu also pointed to a massive seven-figure ad buy that targets Morse by the Senate Majority PAC - the top super PAC supporting Senate Democrats which is aligned with Senate Majority Leader Sen. Chuck Schumer – in praising Morse.

"We need folks with a record of success. Chuck Morse is the candidate, the candidate, to beat Sen. Hassan in office this November and the candidate that Sen. Hassan is most afraid to face,’ Sununu argued. "We have Chuck Schumer spending $3 million… right here in New Hampshire against this guy because they are so afraid. They know Sen. Morse is the candidate most suited to defeat Sen. Hassan soundly this November."

It came as no surprise that Sununu endorsed Morse — who in the state Senate represents Salem, the town were Sununu was raised as a young child — over Bolduc.

Last month, Sununu criticized Bolduc.

"He’s not a serious candidate, he’s really not, and if he were the GOP nominee, I have no doubt we would have a much harder time," Sununu said of Bolduc during a recent interview on a statewide morning radio talk program. "He’s kind of a conspiracy theorist-type candidate."

Bolduc claimed last year that Sununu was a "communist Chinese sympathizer" and that the Sununu family’s business "supports terrorism." While Bolduc has walked back those attacks on the popular governor, he continues to criticize Sununu’s policies during the coronavirus pandemic as "executive overreach." 

Asked whether he questioned whether Bolduc could defeat Hassan in November, Sununu told Fox News "I have full confidence that any Republican is going to win but there’s no doubt Chuck Morse has the best chance, and not just win but win resoundingly. We want to have the coattails."