CNN  — 

Another top Democratic contender for Michigan’s open Senate seat has begun informing colleagues she will take a pass on the race, according to three people familiar with the conversations, narrowing the field for a seat that Democrats are increasingly worried about whether they can keep next November.

Rep. Kristen McDonald Rivet, a freshman Democrat who won a key battleground seat last year, has decided to stay in the House – a decision that is making some Michigan Democrats anxious about their chances of securing a top-tier candidate to go up against a Republican who nearly won the seat last year.

McDonald Rivet had been seriously considering a run and even met with Senate Minority Leader Chuck Schumer this month, according to two people briefed on the meeting. She had been encouraged to run by influential Michiganders, including former Sen. Debbie Stabenow, after another one of the former senator’sother top choices, Pete Buttigieg, chose not to run. Top Democrats, including Schumer himself, also aggressively courted Gov. Gretchen Whitmer, though she repeatedly declined to run, according to people close to Whitmer.

“In this moment, each of us should put ourselves in the position that allows us to do the most good. So I am excited to run for re-election in our highly competitive district, help win back the House, and move an agenda that uplifts the working people in our communities,” McDonald Rivet wrote in a statement.

The fate of Michigan’s Senate seat will be crucial in the 2026 midterms, where Democrats are grappling with key retirements – including Sen. Gary Peters in Michigan – as they attempt to flip enough seats to win back Senate control facing an already challenging map. Trump won the battleground state in two of the last three presidential elections – plus, his own adviser, Chris LaCivita, is working closely with one of the leading potential GOP candidates, former Rep. Mike Rogers, who lost to now-Sen. Elissa Slotkin by fewer than 20,000 votes last year.

Democrats have a long way to go until the August 2026 primary but multiple people told CNN the expected four-person field is now essentially set. And with no clear frontrunner and plenty of angst in their party, some Democrats are so fearful of a bruising and expensive intraparty fight over who will be their nominee that they’re encouraging the Senate Democrats’ campaign arm to consider intervening.

“This is going to be a very messy primary,” one senior Democrat involved in the race told CNN, suggesting that Schumer and his political arm may need to choose sides to avoid harming their eventual nominee.

Rep. Haley Stevens — who had planned to launch at the end of April — plans to announce her run in the coming days, according to two people familiar with her plans. Stevens also met with Schumer last month.

Former Detroit health director Abdul El-Sayed, a progressive who lost in a previous statewide primary for governor in 2018, is expected to enter soon. Already in the race is state Sen. Mallory McMorrow, who aggravated some national Democrats last month by vowing not to support Schumer as leader if she wins the race. A fourth candidate, Joe Tate — a former Michigan House speaker and former NFL player — is also expected to enter.

So far, national Democrats are signaling they will not get involved in the primary, though multiple people closely following the race have also noted that Stevens has hired Christie Roberts, a top party consultant who just launched her own firm after two cycles as the DSCC’s top staffer. (McMorrow has hired another top Democratic strategist: Lis Smith, a former Buttiegig and Obama aide.)

Stevens — who once served as Obama’s top aide on the auto rescue team — first came to Congress in 2018 after flipping a GOP seat. She then beat a fellow Democrat in a redistricting matchup primary in 2022, proving she has the fundraising power, thanks in large part to her ally AIPAC, to get through expensive races.

AIPAC has signaled to Democrats that they intend to spend heavily for Stevens in the primary, according to two people familiar with the plans. It would a big move for the pro-Israel group, which does not typically get involved in state-wide races.

Even people close to Stevens, however, privately worry about her in such a lengthy primary on a national stage. They point to moments that have invited scrutiny, such as her handling of a contentious town hall focused on gun violence in 2019 or a now-famous 2020 floor speech where she shouted over the gavel of her own party to make a point about Covid.

Sen. Gary Peters, who is vacating the seat next year, told CNN he plans to be “fully engaged” in the election to make sure Democrats keep the seat. He does not plan to endorse a candidate in the primary but touted the “very strong bench of young, dynamic folks in Michigan” who he expects to run.

“I want to be absolutely sure that we hold a seat in Democratic hands,” Peters said, who added that he believes anti-Trump sentiment will help fuel his party into wins in Michigan and other key states in 2026.

“I’m confident we’re gonna have a lot of backlash next year. It’s gonna be a good Democratic year.”

This story has been updated with additional details.

CNN’s Lauren Fox and Veronica Stracqualursi contributed to this report.