How 2024 GOP candidates tried to win Chris Sununu's potentially crucial support: Reporter's notebook

After New Hampshire Gov. Chris Sununu opted out of throwing his hat into the race for the White House this summer, he took on a new role: potential kingmaker in the Republican primary -- at least for his state's famously independent swing voters.

"If I make a decision to get behind a candidate, I'm gonna get behind a candidate. It's not an endorsement. It's really a movement that this country is looking for," Sununu said in November, at an event with former South Carolina Gov. Nikki Haley.

As it turns out, the candidate he spoke of was her.

The governor plans to publicly back Haley on Tuesday night, sources familiar told ABC News, in a shake-up in the final weeks before voting in the state's Jan. 23 primary.

Haley and other primary hopefuls have for months been trying to persuade Republican voters that they are the better choice for the party's presidential nomination over the front-runner, former President Donald Trump, who remains hugely popular in polling despite his controversies and legal troubles. (He denies wrongdoing.)

Sununu, a vocal Trump critic within the GOP, didn't join the 2024 race because he felt that a crowded field could help Trump rather than hurt him.

Instead, Sununu has used his standing in New Hampshire to help bolster some of Trump's rivals.

Before deciding to endorse Haley, Sununu publicly narrowed his choices down to her, former New Jersey Gov. Chris Christie -- a friend -- and Florida Gov. Ron DeSantis.

"They are all working hard trying to really coalesce the vote and the opportunities here in New Hampshire," Sununu said in November.

He repeatedly appeared with each of the three candidates, often relying on a familiar template to help shepherd the hopefuls on the campaign trial.

When introducing Haley or Christie or DeSantis, after touting their successes, Sununu often highlighted the things he believes are important to New Hampshire. One of those things includes how much time the candidates have spent in the state.

"It's safe to say Chris Christie has spent more time pounding more pavement, wearing through more soles of shoes in the 603, than anybody else. And we're very appreciative of that," Sununu said last month.

He offered almost exactly the same remarks about Haley a week later.

As much as Sununu publicly dangled a carrot in front of the presidential hopefuls, they stressed their desire to win his support, too.

"Chris has been a friend of mine for a long time. I hope to have the chance to work with him, but nobody's endorsement is going to be dispositive here," Christie said in November.

Haley once even put Sununu on the spot, asking when he would be ready to make his endorsement.

"Getting closer every day. Getting closer every day," he said then.

During one week in November, while all three campaigns were in the state, aides and advisers raced to announce that the governor would be by their side even as Sununu balanced a busy week of official duties.

Campaign aides also jockeyed to be sure their candidate maximized their time in front of the New Hampshire governor -- proposing one-on-one moments ahead of an event, like a meeting in a room next door or at a loading dock, where they would remain out of the public eye.

Some staffers demanded their candidate and Sununu share the same car to an event to allow for more candid time together.

In the weeks and months before Sununu made his decision, the campaigns around him wondered how best to try to read his mind or get a check on where he was leaning -- and how to get him messages.

Journalists assigned to cover New Hampshire weren't left out of the guessing game: Some campaign aides often sought to pump reporters for the latest crumb on Sununu's endorsement plans.

A few aides tried to play the long game, staying distant and remaining hopeful, feeling that the more they badgered Sununu's office, the more they actually hurt their own chances.

Sununu ultimately ending up spending far more days with Haley and Christie than with DeSantis and was often seen laughing with Christie or smiling with Haley -- although Christie said in a podcast appearance on Tuesday that he had no advance notice of Sununu's choice.

Despite the circus-like energy surrounding the whole affair, Sununu has said he wants his support to have a real effect on the race.

Some voters agree he has sway.

"I have a lot of faith in Sununu," said Christy Carlson, an undecided voter from Merrimack, New Hampshire. "So whoever he does get behind that endorsement means a lot to me. That'll be big."

Haley, now the pick, faces some challenges: She trails Trump by double digits in 538's polling average.

"I want to make sure it's impactful," Sununu told ABC News' Rachel Scott in late November. "I want to help the campaign as best I can. It's about a movement. How do you create a movement and excitement, something that's really connecting to the folks, specifically in New Hampshire?"