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Retiring Sen. Gary Peters, D-Mich., has abandoned his neutrality in Michigan's high-stakes Democratic Senate primary, backing U.S. Rep. Haley Stevens as party leaders rally to stop progressive rival Abdul El-Sayed from winning the nomination.

Peters, who is retiring after two terms in the Senate, announced the endorsement Monday, saying Stevens "will be ready on day one to fight for Michigan." The move reverses his position from late May, when he told The Associated Press he planned to stay neutral in the Aug. 4 primary.

Democrats are eager to keep the Michigan seat as they try to win back the Senate majority, and many party leaders have lined up behind Stevens, a four-term congresswoman they see as a stronger general election candidate.

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Rep. Haley Stevens gestures while speaking with reporters

Michigan U.S. Sen. candidate, Rep. Haley Stevens, D-Mich., speaks with media after a debate at WoodTV studios on Tuesday, July 7, 2026, in Grand Rapids, Mich. (AP Photo/Kristen Norman)

Stevens has centered her campaign on manufacturing, jobs and Michigan's auto industry. El-Sayed, a former Michigan health director who has never held elected office, has run on a more progressive platform that includes Medicare for All and campaign finance reform. He has also made the war in Gaza a central issue in his campaign, highlighting a divide that has surfaced within the Democratic Party.

Sen candidate Abdul El-Sayed gestures while speaking with reporters

Michigan U.S. Sen candidate, Abdul El-Sayed, speaks with media after a debate at WoodTV studios on Tuesday, July 7, 2026, in Grand Rapids, Mich. (AP Photo/Kristen Norman)

Peters' endorsement comes weeks after State Sen. Mallory McMorrow ended her campaign, leaving Stevens and El-Sayed as the only major Democratic candidates in the race.

"Senator Peters knows what it takes to win in Michigan, and he knows what Michigan needs from our next U.S. Senator: grit, effectiveness, hard work, and Michigan common sense," Stevens said in a statement. "I am honored to have his support."

Peters has won two Senate elections in Michigan and previously chaired the Senate Democrats' campaign committee during the 2022 and 2024 election cycles.

Sen. Gary Peters of Michigan, the chair of the Democratic Senatorial Campaign Committee, is interviewed by Fox News Digital, at the Democratic National Convention in Chicago, on August 19, 2024

Sen. Gary Peters of Michigan, the chair of the Democratic Senatorial Campaign Committee, is interviewed by Fox News Digital, at the Democratic National Convention in Chicago, on August 19, 2024 (Fox News - Paul Steinhauser)

His endorsement follows similar backing for Stevens from Senate Democratic Leader Chuck Schumer, D-N.Y., Sen. Ruben Gallego, D-Ariz., and Sen. Catherine Cortez Masto, D-Nev. El-Sayed has been endorsed by Sen. Bernie Sanders, I-Vt., and Sen. Chris Van Hollen, D-Md.

The campaign has become increasingly personal in recent weeks.

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El-Sayed has criticized Stevens over tens of millions of dollars in outside spending supporting her campaign, including money from the American Israel Public Affairs Committee. Stevens has accused El-Sayed of refusing to release his personal financial records. During a July 7 debate, both candidates accused the other of running a negative campaign.

The Democratic nominee will likely face Republican Mike Rogers, a former Michigan congressman who is running unopposed for his party's nomination. It is expected to be among the nation's most expensive and closely watched Senate contests in November.

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Michigan has taken on added importance for Democrats after turmoil erupted in another key Senate race in Maine, where Democratic nominee Graham Platner withdrew following a sexual assault allegation. The unexpected vacancy has complicated the party's efforts to challenge Republican Sen. Susan Collins, increasing the pressure to avoid setbacks in other battleground states such as Michigan.

The Associated Press contributed to this report.