LANSING, Mich. — Michigan Sen. Debbie Stabenow, a member of the Democratic leadership, announced Thursday that she will not run for a fifth term in 2024, opening up a seat in the key battleground state.

The news likely comes as a shock to many Democrats in the state because Stabenow had not previously indicated that she would not seek reelection.

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

Democrats will face a test to find a candidate with the broad support of Stabenow, first elected to the Senate in 2000. She has easily won reelection since then.

She joined the House in 1996. In 2000, she made history by becoming the first woman to be elected senator in Michigan, defeating a Republican incumbent. She turned back GOP challenges in 2006 and 2012 and defeated political newcomer John James, by 6.5 percentage points in 2018. James was elected to the House in November.

The 72-year-old Stabenow, of Lansing, is the longest-serving member of the state’s congressional delegation. She recently was elevated to chair of the Democratic Policy and Communications Committee, making her the No. 3 ranking party leader, and heads the Senate Agriculture, Nutrition and Forestry Committee.

Stabenow most recently has been involved in bipartisan legislation aimed at increasing oversight of cryptocurrencies. She has also led efforts to expand and increase funding for mental health care both nationally and in Michigan.

The announcement is expected to make Michigan’s 2024 Senate race one of the most competitive in the country.

While the current political climate in Michigan favors Democrats following a midterm election where they flipped the state House and Senate, the state is still expected to be one of the nation’s premier battlegrounds in the 2024 presidential election.

Only one Michigan Republican has held a seat in the Senate in the past 40 years.

The date of Michigan’s primary is yet to be finalized after the Democratic National Committee rule-making arm voted to move Michigan up in the party’s presidential primary calendar for 2024. If the full DNC approves the plan, as expected, Michigan would be the fifth state to vote in the primary process on Feb. 27.

The Republican National Committee has already set their primary schedule and Michigan is not in the first five states. If Michigan Republicans were to move their primary before March 1 to match the Democrat’s plan, they could be significantly penalized by the national Republican Party.