Democrats Fume After Defeated Senate Candidate Backs G.O.P. Rival in Michigan Democrats Fume After Defeated Senate Candidate Backs G.O.P. Rival in Michigan

Intraparty tensions boil over just days before the midterms as Representative Haley Stevens endorses Republican Mike Rogers over her former primary opponent, Dr. Abdul El-Sayed.

DETROIT — Just days before the midterm elections, Michigan’s U.S. Senate race was rocked by a major intraparty defection. Representative Haley Stevens endorsed Republican nominee Mike Rogers, breaking ranks with her own party and infuriating fellow Democrats who fear the move could jeopardize a crucial Senate seat.

The surprise endorsement arrived on Sunday after a bitter breakdown in relations between Ms. Stevens and Dr. Abdul El-Sayed, the Democratic nominee who narrowly defeated her in an August primary. Tensions had steadily escalated over policy disagreements concerning Israel and disputes over campaign advertising. Efforts by senior party figures, including Representative Debbie Dingell and Representative James E. Clyburn of South Carolina, ultimately failed to broker a lasting peace ahead of Sunday campaigning.

The fallout was swift and severe. Senate Democratic Leader Chuck Schumer denounced the endorsement as a “despicable betrayal,” while Republicans welcomed the development as a potential source of momentum. President Trump praised Ms. Stevens during a rally in Iowa, and the endorsement provided a welcome headline for the G.O.P. in a cycle where recent New York Times/Siena polling has shown Democrats holding a sizable lead in Michigan and competitive positions across several battleground states.

Despite the high-profile distraction, Dr. El-Sayed brushed off the maneuver while speaking with reporters, maintaining that his campaign remains focused on key issues that matter to Michigan voters as the election approaches.