Sen. Joe Manchin, D-W.Va., chairs a hearing of the Senate Energy and Natural Resources Committee on the health of the electrical power grid in June. Manchin has announced he won’t seek reelection in 2024, giving Republicans a prime opportunity to pick up a seat in the heavily GOP state. J. Scott Applewhite/Associated Press, file

CHARLESTON, W.Va. — Democratic Sen. Joe Manchin of West Virginia announced Thursday that he won’t seek reelection in 2024, giving Republicans a prime opportunity to pick up a seat in the heavily GOP state.

Manchin, 76, said he made the decision “after months of deliberation and long conversations” with his family.

“I believe in my heart of hearts that I have accomplished what I set out to do for West Virginia,” he said in a statement. “I have made one of the toughest decisions of my life and decided that I will not be running for re-election to the United States Senate, but what I will be doing is traveling the country and speaking out to see if there is an interest in creating a movement to mobilize the middle and bring Americans together.”

His decision to step down, while not totally unexpected, severely hampers Democratic hopes of holding on to the coal country seat and marks the end of an era for West Virginia, which voted reliably blue for decades before flipping red and becoming one of former President Donald Trump’s most loyal states. For the last few years, Manchin has been the only Democrat elected to statewide office in West Virginia.

But his statement also fuels growing speculation that Manchin harbors national political ambitions. In recent months, he has teased a 2024 presidential campaign, possibly as an independent candidate, although it’s unclear what his voter base would be. Along those lines, a group pushing for Manchin to partner with retiring Utah Sen. Mitt Romney to seek a third-party presidential bid filed paperwork to form a formal draft committee with the Federal Election Commission on Thursday.

Manchin’s announcement also reinforces the challenges Democrats will have in keeping their 51-49 Senate majority. Even before Manchin said he was stepping down, 2024 was shaping up to be a tough election cycle for Senate Democrats. The party will be forced to defend 23 seats, including three held by independents and three held by Democrats in states won by Trump in 2020, compared to just 10 seats for Republicans.

Republican challengers have long been clamoring for Manchin’s seat. GOP Rep. Alex Mooney jumped into the race less than two weeks after winning his fifth term in the House in November 2022. Hugely popular two-term Republican Gov. Jim Justice joined the Senate race earlier this year and was endorsed by Trump, only increasing the challenges for Manchin as he considered whether to seek reelection.

Justice noted in a statement Thursday that he and the senator “have not always agreed on policy and politics.”

“But we’re both lifelong West Virginians who love this state beyond belief, and I respect and thank him for his many years of public service,” the governor said.

The draft committee pushing a Manchin-Romney ticket is planning to launch publicly next week along with a new website titled “America Back on Track,” according to a person with direct knowledge of the committee who spoke to The Associated Press on the condition of anonymity to disclose internal planning ahead of the launch.

Initially, the draft effort plans to raise $1 million for a budget to commission polling to show that there is a path to victory for a Romney-Manchin ticket as part of the No Labels movement, according to the person.

Romney and Manchin have not signed onto this effort, the person said. But the group expects to build out presidential campaign infrastructure for Romney and Manchin and ultimately court No Labels delegates to win the nomination at its March 2024 convention in Dallas.

No Labels praised Manchin as a “tireless voice for America’s commonsense majority” in a statement Thursday.

“We will make a decision by early 2024 about whether we will nominate a Unity presidential ticket, and who will be on it,” the organization said.

Manchin, a conservative Democrat, was both a critical vote and a constant headache for his party in the first two years of President Biden’s term. When the Senate was split 50-50 and Democrats controlled it by virtue of Vice President Kamala Harris’ tiebreaking vote, Manchin leveraged his political power to shape legislation to his liking.

Along with Sen. Kyrsten Sinema of Arizona, a Democrat who switched to an independent after last year’s midterms, he helped water down much of Biden’s social spending agenda. He has frequently clashed with members of his own party over his strong support for coal and other fossil fuels.

Days before last year’s midterms, he blasted Biden for being “cavalier” and “divorced from reality” after vowing to shutter coal-fired power plants and rely more heavily on wind and solar energy in the future. He demanded a public apology from Biden, and the White House acquiesced by issuing a statement saying the president “regrets it if anyone hearing these remarks took offense.”

Biden issued a statement Thursday praising Manchin for his decades of public service.

“For more than forty years – as a state legislator, a Secretary of State, a Governor, and a Senator – Joe Manchin has dedicated himself to serving the people of his beloved West Virginia. During my time as Vice President and now as President, Joe and I have worked together to get things done for hardworking families,” Biden said.

Manchin’s announcement comes just a year after Democrats increased their Senate majority to 51-49 by flipping a Republican-held seat in Pennsylvania. The practical effect of that victory was giving Democrats the ability to pass bills while losing one vote within their caucus – zapping Manchin’s power to singlehandedly thwart some of his party’s priorities.

Manchin regained some of that influence after Sinema switched parties, though she made clear that she would not caucus with Republicans. Sinema is also up for reelection in 2024 but has not yet announced her plans.

Manchin entered the Senate after winning a special election in 2010 following the death of Robert C. Byrd. He won reelection in both 2012 and 2018, with the latter campaign his toughest in his three-plus decades in West Virginia politics. He defeated Republican state Attorney General Patrick Morrisey by just over 3 percentage points.

Registered Democrats outnumbered Republicans during Manchin’s first two Senate campaigns, but things have changed since then. Now, about 40% of registered voters are Republicans, compared with 31% for Democrats and about 24% with no party affiliation.

Both chambers of the Legislature have Republican supermajorities, and Trump overwhelmingly won the state in 2016 and 2020.

Manchin’s penchant for not following fellow Democrats on some key votes was a cause of angst and bruised relationships within his own party. It even prompted independent Sen. Bernie Sanders to suggest that he would support a 2024 primary challenger to Manchin.

Manchin’s split with the White House prompted Senate Republican leader Mitch McConnell of Kentucky to publicly invite him to join the GOP. Manchin held firm there, too, insisting that he saw himself as a Democrat.

During Manchin’s first two terms in the Senate, West Virginia lost thousands of coal jobs as companies and utilities explored using other energy sources such as natural gas, solar and wind. Manchin later promoted the Biden administration’s plans to involve the state in the development of clean energy. But his push to speed permits for natural gas pipelines and other energy projects – including a planned pipeline in his home state – failed.

Under Trump, Manchin was the only Democrat to vote for the confirmation of Supreme Court Justice Brett Kavanaugh in 2018 and among three Democrats to support nominee Neil Gorsuch in 2017. But he voted with Democrats on other key issues, including a failed 2017 effort by Republicans to repeal the Affordable Care Act passed under President Barack Obama.

In a statement Thursday, Manchin’s West Virginia colleague Republican U.S. Sen. Shelley Moore Capito thanked him for his years of service.

“I’ve enjoyed serving alongside you – our senior senator,” she said. “And as you said, we still have much work ahead of us. Thank you for your friendship, Joe. I look forward to that continuing.”

West Virginia Democratic Party Chair Mike Pushkin called Manchin “a larger-than-life figure in the United States Senate” and said his “name has been synonymous with West Virginia politics and government” for 41 years.

Associated Press writers Steve Peoples in New York and Farnoush Amiri in Washington contributed to this report.