Gov. Chris Sununu of New Hampshire, a Republican, surprised his party on Tuesday by announcing that he would not run for U.S. Senate next year, rejecting a full-court press from national Republicans who tried to recruit him to compete for a Democratic-held seat that the G.O.P. believed could determine control of the Senate.
Instead, Mr. Sununu announced at a news conference that he would seek a fourth two-year term as governor, a job in which he said he could make more of a difference than in Congress, where “too often doing nothing is considered a win.”
“My responsibility is not to the gridlock and politics of Washington,” he said. “It is to the citizens of New Hampshire.”
Republican leaders had seen a Sununu challenge to Senator Maggie Hassan, a Democrat, as one of their best shots to upend the Senate’s 50-50 partisan split, which gives Democrats control with the tiebreaking vote of Vice President Kamala Harris.
At a Republican gathering in Las Vegas over the weekend, where Mr. Sununu spoke, Senator Ted Cruz of Texas urged attendees to lean on Mr. Sununu. “Every person here needs to come up to Chris and say, ‘Governor is great but you need to run for Senate,’” Mr. Cruz said. “Because this man could single-handedly retire Chuck Schumer as majority leader of the Senate.”
Republicans in Washington were taken off guard by Mr. Sununu’s decision. Senator Mitch McConnell, the minority leader, who had personally lobbied Mr. Sununu to run, was given no heads up about his decision, according to Josh Holmes, an adviser to Mr. McConnell. The Republican Governors Association “had no idea either,” Mr. Holmes said.
But a longtime Republican consultant in New Hampshire, Dave Carney, said Mr. Sununu’s decision was not a surprise to those who know him. “The gridlock in D.C. is a hard sell,” Mr. Carney said.
The decision was perhaps most surprising given that the political climate ahead of the midterms has shifted in Republicans’ favor after their gains in races across the country last week. Although the 2022 Senate map favors Democrats, with their most vulnerable candidates running in states that President Biden won, his narrow victories in places like Arizona and Georgia make first-term Democrats there potentially vulnerable. Democrats’ best shot at picking up a Senate seat is in Pennsylvania, the only Republican-held seat that is now open in a Biden-won state.
In New Hampshire, the most serious declared Republican Senate candidate so far is Donald C. Bolduc, a retired Army general. He lost a G.O.P. primary last year to a Trump-endorsed challenger, who ultimately lost against New Hampshire’s senior senator, Jeanne Shaheen, a Democrat.
Republicans consider Ms. Hassan, who won her seat by about 1,000 votes in 2016, to be among the most vulnerable Democratic senators next year.
“Maggie dodged a bullet for sure,” said Irene Lin, a Democratic consultant who has worked in New Hampshire.
With Mr. Sununu sitting out the race, speculation turned to former Senator Kelly Ayotte, who lost the seat to Ms. Hassan.
Mr. Sununu, 47, was re-elected to a third two-year term in 2020 with 65 percent of the statewide vote. That was 20 percentage points better than what former President Donald J. Trump received in losing New Hampshire to Mr. Biden. Unlike other Republican governors of blue states, such as Maryland or Massachusetts, Mr. Sununu supported Mr. Trump’s re-election, declaring at one point, “I’m a Trump guy through and through.”
A University of New Hampshire poll in September found that support for Mr. Sununu was eroding, but still high. Fifty-seven percent of New Hampshire adults approved of the job the governor was doing, including his handling of the Covid-19 pandemic. But the share of independents who approved of his performance as governor fell for the third consecutive month.
Blake Hounshell contributed reporting.