Things just got a whole lot more interesting in New Hampshire politics. Just below the presidential churn, the governor’s race in the politically quirky Granite State has some superjuicy drama percolating — the kind that offers a vivid reminder of just how much trouble Donald Trump stands to cause for his party in 2024.

Gov. Chris Sununu, currently enjoying his fourth two-year term, recently announced that he would not run for re-election next year. This instantly gave Democrats their best shot at flipping a governorship from red to blue in 2024, and the race is now rated as a tossup. Quick as a bunny, Republican contenders began hopping into the field, and both parties started gearing up for a brawl.

Of the candidates so far, the best known is the former senator Kelly Ayotte. Like Mr. Sununu, Ms. Ayotte is from the more moderate, pragmatic, bipartisan end of the Republican spectrum — as you might expect in this staunchly independent, politically purple state. Elected to the Senate in 2010, she was considered a serious up-and-comer in the party until, with a little help from Mr. Trump’s lousy coattails, she narrowly lost her 2016 re-election race against the Democrat Maggie Hassan.

It’s hard to know precisely how much of a drag Mr. Trump, who also lost New Hampshire that year, exerted on Ms. Ayotte. But the senator’s wild waffling over Mr. Trump’s fitness for office surely didn’t help: Did she see as him a role model? “Absolutely.” Oops, make that no! Would she endorse his candidacy? Um, not really. Did she personally support him? Yes. Wait, no!

The voters of New Hampshire were unimpressed.

Seven years later, Ms. Ayotte is looking to make a comeback. Unfortunately for her, so is Mr. Trump, who may be popular in deep red states but will be a source of agita for Ms. Ayotte and other Republicans in swing states who might have to share the ticket with him. Republicans are hopeful about picking up Senate, House and governors’ seats in 2024, but they have barely started to contend with how the once-and-aspiring president could complicate things for down-ballot candidates.

Nowhere is this clearer than in New Hampshire, a key presidential battleground. The state’s Trump-infected political landscape looks even more treacherous in 2024 than it did in 2016. Not just because of the former president’s latest campaign, which is shaping up to be even nastier and more divisive than his first two, but also because of Mr. Sununu’s high-profile crusade to tank that campaign.

One of the nation’s most popular governors and one of his party’s most prominent Trump critics, Mr. Sununu has grown increasingly adamant that his party must move beyond the 45th president, and he has publicly pledged to work against Mr. Trump’s nomination. If Mr. Trump is the nominee in 2024, “Republicans will lose again. Just as we did in 2018, 2020 and 2022. This is indisputable, and I am not willing to let it happen without a fight,” Mr. Sununu wrote in The Washington Post last month.

This move may burnish Mr. Sununu’s independent rep nationwide. (He is seen as a future presidential player.) But it only complicates life for many down-ballot Republicans in the state. Especially ones, like Ms. Ayotte, who have a somewhat … troubled history with the fealty-obsessed Mr. Trump.

For the G.O.P., the New Hampshire governor’s office is one of the shrinking number of outposts where a pragmatic, old-school breed of Republican leader has been able to thrive in the midst of the party’s MAGAfication. Republicans felt confident Mr. Sununu had the juice to win, no matter who topped the ticket next year. Any other Republican is a shakier bet for winning the independent and crossover votes needed to win statewide in New Hampshire. The governor’s departure is being talked about as yet another step in the party’s ideological constriction.

Although broadly popular, Mr. Sununu is not beloved in New Hampshire’s conservative circles. His anti-Trump mission will do nothing to improve this. “I think Sununu is trying to dance the same tightrope I am and a lot of us are: being very forceful about the fact that we need a new nominee and yet trying not to take too big of a dump on the former president,” said Jason Osborne, the Republican leader of the state House and one of Ms. Ayotte’s early endorsers.

Fancy footwork aside, the Trumpnunu rift is going to make it harder for the governor’s aspiring successors to avoid getting sucked into the Trump vortex — the dangers of which Ms. Ayotte knows too well. She is already trying to get out ahead of the issue, asserting that she will support whoever winds up the party’s standard-bearer.

“I do wonder whether she’s going to hold to that line of, ‘Hey, that’s between Sununu and Trump,’” said Dante Scala, a professor of political science at the University of New Hampshire. “She may be able to do that for some time.”

But as campaign season heats up, look for Ayotte et al. to be increasingly pressed to clarify their views on the whole mess. (Trust me: Intraparty feuding is catnip for political journalists.) Staying out of the muck will very likely require elaborate tap dancing on a tightrope while juggling hot potatoes.

The situation will be even thornier for whomever Mr. Sununu decides to endorse — which, at this point, is expected to be Ms. Ayotte. Sure, a popular governor’s nod in the race to succeed him will serve as a vote of confidence in the eyes of many. But it could also “fire up the conservative base even more” to undermine his pick, said Mike Dennehy, a G.O.P. strategist in the state. The territory is “more complicated than in 2016,” he asserted. And some think it would be best for the governor to delay endorsing until much later in the game.

All of this, mind you, is piled on top of Ms. Ayotte’s specific challenges as a candidate. (Pro-life in a pro-choice state post-Dobbs? Oof.) And the basic political disposition of New Hampshire. “In general, it has become a slightly uphill battle to beat Democrats,” observed Mr. Scala.

Stay tuned. As with so much in Mr. Trump’s Republican Party, this promises to be quite the show.