Michigan senator Debbie Stabenow, a member of the Democratic leadership, announced on Thursday that she would not seek re-election in 2024, setting the stage for a fierce contest to claim an open seat in a critical midwestern battleground state.

Stabenow, 72, is the first Senate Democrat to announce her retirement ahead of 2024, when the party will try to defend its razor-thin majority by fending off challenges to incumbents in several states that former president Donald Trump won.

But Democrats delivered a strong performance in Michigan last year and expressed confidence that the seat would remain in the party’s control.

“Inspired by a new generation of leaders, I have decided to pass the torch in the US Senate,” Stabenow said in a statement on Thursday. “I am announcing today that I will not seek re-election and will leave the US Senate at the end of my term on 3 January 2025.

“Under the cloud of unprecedented threats to our democracy and our basic freedoms, a record-breaking number of people voted last year in Michigan. Young people showed up like never before. This was a very hopeful sign for our future,” she said.

Stabenow’s decision not to seek a fifth term after serving two decades in the chamber immediately turned the race for Michigan’s open Senate seat into one of the most competitive in the nation. Republicans welcomed the development as a sign that Democrats’ hopes of maintaining their one-seat majority were already fading.

“We are going to aggressively target this seat in 2024,” said Mike Berg, communications director for the National Republican Senatorial Committee, the campaign arm of Senate Republicans. “This could be the first of many Senate Democrats who decide to retire rather than lose.”

Senate Democrats face a punishing electoral map next year. They are defending nearly a quarter of the seats in the Senate, many of them in competitive states as well as in red states like Ohio, Montana and West Virginia. By contrast, no Senate Republican faces re-election in a state Joe Biden won.

But their prospects have improved in Michigan since Trump won the state in 2016. Biden won the state in 2020. And two years later, fury over efforts to ban abortion in Michigan in the wake of the supreme court decision overturning Roe v Wade propelled Democrats to victory up and down the ballot in the state.

In a statement, Senate majority leader Chuck Schumer praised Stabenow as the embodiment of the “true Michigan spirit” and thanked her for her years of service in Congress and her leadership within the caucus. “With Debbie’s help, and the strong Michigan Democratic party she helped build, Debbie and I are confident Democrats will retain the seat,” he said.

Speculation began to swirl about who Democrats might nominate to replace Stabenow. Attention immediately turned to Democratic congresswoman Elissa Slotkin who clinched a decisive victory in November in one of the most competitive House races that cycle. Other possible contenders included congresswoman Haley Stevens, transportation secretary Pete Buttigieg, the former mayor of South Bend, Indiana, who recently moved to Michigan to be closer to his husband’s family.

In a statement, Buttigieg called Stabenow a “force in the Senate” but said he was “not seeking any other job”.

Michigan governor Gretchen Whitmer, who resoundingly won re-election in November, praised Stabenow as a “champion for Michigan” while indicating that she was not interested in running for the seat. “As governor of this great state for the next four years, I look forward to working with [Stabenow] through the end of her term and beyond in however she serves our state next,” Whitmer said in a statement, emphasizing her plans to serve a full four-year term.

Other Michigan officials whose names have been raised include Lt governor Garlin Gilchrist, secretary of state Jocelyn Benson, attorney general Dana Nessel as well as state senator Mallory McMorrow, who drew interest after a forceful rejoinder to Republican accusations that Democrats want to “groom” children went viral.

Stabenow first joined Congress in 1996 after serving in the Michigan state legislature. In 2000, she became the first woman to represent Michigan in the US Senate. Stabenow climbed through the ranks, becoming a member of Democratic leadership and chair of the agriculture committee. In 2018, she turned back a well-funded and closely-watched challenge from Republican John James, who is seen as a rising star on the right.

James was elected to the House in November and is considered a potential contender for the Republican Senate nomination. Other possible Republican candidates are former congressman Peter Meijer, a relative moderate who lost his seat last year as well as Tudor Dixon, a Trump loyalist who was defeated by Whitmer in the race for governor.

In her statement, Stabenow reflected on the progress Michigan women had made in politics since she first ran for office in 1974, at the age of 24.

“This began years of breaking barriers, blazing trails and being the ‘first’ woman to reach historic milestones as an elected official,” she said, adding: “But I have always believed it’s not enough to be the ‘first’ unless there is a ‘second’ and a ‘third’…”