Senator Gary Peters of Michigan announced on Tuesday that he would not run for re-election in 2026, forcing Democrats to defend an open seat in a battleground state that President Trump won in 2024 and making the party’s already tough path to a Senate majority even tougher.
Mr. Peters, who was first elected in 2014, won re-election in 2020 by less than two percentage points. His decision not to seek a third term will set the stage for another key contest next year in a state that will already have a wide-open governor’s race, with Gov. Gretchen Whitmer departing because of term limits.
Mr. Peters had served as the chairman of the Democratic Senatorial Campaign Committee for the last two election cycles.
In a video about his choice on Tuesday morning, Mr. Peters said, “I always knew there would come a time to pass the torch to the next generation of public servants and allow them the opportunity to bring fresh energy and ideas to our nation’s capital.”
At 66, Mr. Peters is relatively young for a senator stepping down. He had previously served three terms in the House and was also in the Navy Reserve.
In the video, Mr. Peters said that the “most important chapter in my life is a work in progress,” including being a new grandfather.
The path for Democrats to take back the Senate in 2026 was already steep. Republicans now hold a majority with 53 seats, and with Vice President JD Vance serving as the tiebreaking vote, Democrats would need to win four seats.
The party has few pickup opportunities and is already set to defend the seat of Senator Jon Ossoff in Georgia.
Democrats successfully held a Democratic seat in Michigan last year, when Elissa Slotkin, then a Democratic House member, defeated former Representative Mike Rogers, a Republican. It was one of the most closely fought races in the nation, with Ms. Slotkin prevailing by fewer than 20,000 votes and roughly 0.3 percentage points.
It was not immediately clear how the open Senate seat might scramble the governor’s race, which was already crowded and competitive, though Ms. Whitmer quickly ruled out a run for Mr. Peters’s slot in an interview on “The View” on Tuesday.
“Three letters: N.F.W.,” she said, using an abbreviation for “no way” with an expletive in the middle. “I am not going anywhere. I’ve got two more years on my term. I’ve got a lot of things I want to get done as governor. What comes after that, I don’t know yet. I really don’t.”
Jocelyn Benson, the Democratic secretary of state of Michigan, announced a bid for governor last week, while Mayor Mike Duggan of Detroit, a longtime Democrat, is running for governor as an independent. Aric Nesbitt, the Republican leader in the Michigan Senate, has also announced.
Other potential candidates include prominent Democratic state politicians like Lt. Gov. Garlin Gilchrist II and former Transportation Secretary Pete Buttigieg, though Mr. Buttigieg is taking a “serious look” at a Senate bid, according to a person with knowledge of his thinking who insisted on Tuesday on anonymity to discuss the private deliberations.
Mr. Buttigieg was born and raised in South Bend, Ind., where he was mayor when he sought the Democratic presidential nomination in 2020. But he moved his young family to Michigan, a state with brighter electoral prospects for an ambitious Democrat, while serving in the Biden administration. His team said at the time that he moved for family reasons, noting that his in-laws live in Michigan and assist with child care.
There is no shortage of prominent Michigan Democrats considering higher office, including Representative Haley Stevens, 41, who represents some of Detroit’s suburbs, and Representative Hillary Scholten, from the Grand Rapids area. The state attorney general, Dana Nessel, also is subject to term limits and cannot seek re-election in 2026.
Mallory McMorrow, a state senator who won Democratic acclaim in 2022 with a speech defending liberal values while identifying herself as a “straight, white, Christian, married suburban mom,” said she had not ruled out a run for either governor or for the Senate.
“I’m taking a serious look at both the governor and Senate seats and plan to have many conversations over the coming days to see where I might be best suited to serve Michiganders,” she said in a text message on Tuesday.
The Republican bench in Michigan is thinner, as the party has struggled in statewide races. Representative John James, who is in his second term in the House, lost back-to-back races for the U.S. Senate in 2018 and 2020.
Representative Bill Huizenga, a Republican who has served in the House since 2011, is considering a run for the open Senate seat, according to a person with knowledge of his thinking.
“No Republican has won a Michigan Senate race in 30 years — including last cycle when Democrats won an open Senate seat even as Trump won the state — and Democrats will continue to hold this seat in 2026,” David Bergstein, a spokesman for the campaign arm of Senate Democrats, said in a statement.
