Democratic congresswoman Haley Stevens stunned party officials on Sunday by endorsing Republican Mike Rogers in Michigan's US Senate race, the Associated Press reports. Stevens lost the August Democratic primary to Abdul El-Sayed by a slim margin. El-Sayed now faces Rogers for the seat held by retiring Democrat Gary Peters.

Stevens backed Rogers after attending a Detroit church service with him, the AP reports. Her longtime chief of staff resigned, and more staff are expected to follow, according to a person familiar with the matter. "We are shocked and heartbroken," the aide said. In a CNN interview on Sunday night, Stevens said, "This is a weight off my shoulders." Congresswoman Debbie Dingell called it "one of the most painful interviews I have watched."

State party chair Curtis Hertel said Stevens "is not a current member of the Michigan Democratic Party, nor will she be in the future," the AP reports. El-Sayed said, "None of this matters." Senate Democratic Leader Chuck Schumer called it a "despicable betrayal."

Rogers said on Saturday that his campaign's internal model has him ahead in early returns, the New York Post reports. "We're ahead on the early returns so that's very good for us, almost by seven percent," he said. The Post notes there is no data on how early voters cast their ballots, only their party and voting history. Democrats lead the early ballots 51% to 39% by party, according to NBC News data cited by the Post. El-Sayed leads Rogers by 3.5 points in the RealClearPolitics polling average, the Post says.

Early voting has been underway since late October, and more than 1.8 million people had voted in Michigan as of Friday, the AP reports.

What we know: Stevens has endorsed Rogers, and Democrats are scrambling ahead of Tuesday's vote.
What we don't: Whether the split will move voters in a close race.