A sitting Michigan Democrat crossed party lines days before the election, triggering a bitter intra-party revolt with national stakes.

• Democratic Congresswoman Haley Stevens endorsed Republican Mike Rogers for Senate over her own party's nominee, Abdul El-Sayed, just one day after privately promising allies she was still backing him.
• Her entire staff of eight years resigned in protest, and former colleagues and friends publicly accused her of betrayal and cowardice.
• Critics point out AIPAC poured tens of millions into Stevens's earlier campaign and Elon Musk has spent hundreds of millions backing Republicans this cycle, framing her move as money-driven rather than principled.
• The flip matters beyond one Senate seat because control of the chamber affects future Supreme Court confirmations.
• Rogers himself has a history of inflammatory remarks against Muslim Americans, which critics say undercuts Stevens's stated reason for leaving her own party's candidate.

Outlook: The defection is expected to energize Democratic turnout in Michigan ahead of Tuesday's election, with the Senate seat seen as a toss-up.