“We need that seat,” said Rep. Ann Kuster (D-N.H.), who added she has personally urged Levin not to battle against Stevens and instead run in the tougher seat. “He’s got a well-known name, he has most of the constituents in that district, and all he had to do was work hard, roll up your sleeves. Why work hard against a colleague?”

It’s not just Democrats who think Levin had a chance. GOP groups have previously undisclosed polling that shows the Michigan Democrat could have been competitive in the state’s new 10th District, according to multiple people familiar with internal discussions. The seat includes about two-thirds of Levin’s current constituents, though it also picked up much more GOP ground — which Levin and his supporters have said made it impossible for him to compete there.

Members of Michigan’s congressional delegation have mostly declined to discuss the member-on-member primary in public. Retiring Rep. Brenda Lawrence (D-Mich.) is the only member of the delegation to choose a side.

Rep. Elissa Slotkin, another Michigan Democrat, said she is not weighing in on the primary. But she acknowledged that she considered Levin to be a viable candidate.

“I think certainly an incumbent would’ve had a good shot against Mr. James,” Slotkin said. “There’s no doubt about it, that is a swing district, a tough district. But it’s a tough district for both parties.”

Levin and his allies, however, said he never had a real chance of winning the new seat, which covers turf that former President Donald Trump won by nearly one percentage point in 2020. As a vocal progressive, Levin said his natural choice was to run in the new, bluer 11th District; that includes his hometown of Bloomfield and the town where he and generations of his family grew up.

“I’m running where I live, and I’m very happy about that decision, no regrets,” Levin said in an interview, declaring that he would win the primary and then help the party hold onto the Macomb County seat.

Asked about the calls from several of his colleagues to instead run in the battleground seat, Levin said: “I’m grateful that people think I can do something, but I’m pretty sure on what the best strategy is.”

“It’s a very different district,” Levin said, pointing to the influx of new GOP voters. “I’m very tuned into Macomb County politics, much more than the people that you’re talking to. I have a real sense of how we can win there. And I’m determined for us to win.”

Levin added that as the longtime Macomb County representative, he has spoken to every Democrat who is running or has considered running in the new seat. He’s coordinated with the party’s campaign arm on recruitment as well.

So far, though, some Democrats are worried about their bench in that 10th District seat, even with five candidates now running.

Among the most high-profile candidates is ex-judge Carl Marlinga — who faced federal corruption charges two decades ago, though they were later dropped. Earlier this year, national Democrats even turned to former GOP Mayor Michael Taylor, who opted not to run. Last month, a former state lawmaker and ex-firefighter Henry Yanez jumped into the race, after heavy local recruiting.

GOP campaign operatives, meanwhile, are upbeat about James, who is a former Army ranger turned businessman. James has already lost two bids for Senate, losing Macomb County in 2018 while winning it in 2020. But some Democrats fear he’ll have a better shot in this district’s newest iteration.

And James’ candidacy is a key part of the reason many Democrats pushed so hard for Levin. They argue he would have potentially more name recognition than James the twice-losing Senate candidate, given his family’s dynastic status in Michigan politics.

Both Levin and Stevens were elected in the 2018 Democratic wave. Stevens flipped a red seat after GOP Rep. Dave Trott retired, while Levin replaced his father, former Rep. Sander Levin, who retired after 18 terms. Levin’s uncle also represented the state in the House, making the pair the longest-serving siblings in congressional history.

“I think his name made him the most competitive. He and his family represented Macomb County for decades.” said Lawrence, who retired after her own district was redrawn this cycle. Lawrence, like Kuster, has endorsed Stevens in the primary.

Other senior Democrats, including progressives, also said Levin had a chance to make a huge statement by overcoming the odds to win the 11th District: If he could hold it, he could prove the left’s longtime argument that their brand of politics is palatable in competitive seats.

Levins’ supporters, however, have strongly pushed back on the idea that he could win the race, with his home no longer in the district, even as they said others in the party still could. Other longtime observers of Michigan politics went further, saying in interviews that it might be a tough race for any Democrat to win.

David Mermin, a partner at Lake Research Partners, which has conducted polling on behalf of Levin, said the new district “just doesn’t look promising” for Democrats: “You need a Macomb County-type Democrat.”

Jim Jacobs, who recently retired as president of Macomb Community College and has deep ties to the area, added that “it’s going to be extremely difficult for any Democrat to win the county.”

Democrats’ anxiety around Michigan’s 10th and 11th District races is compounded by the mounting fears across the party that its fragile majority could be wiped out in November. Just in recent days, the party has suffered some redistricting losses, while Biden’s approval rating has continued to sink.

And Michigan, often seen as a critical barometer of political climate, is even more closely watched this year, as it loses a seat altogether in redistricting.

While member-on-member primaries are always bitter, this one has gotten particularly nasty as key factions of the caucus have come out for opposing candidates. The Congressional Progressive Caucus is backing Levin, while Stevens has won support from her own moderate New Democrat Coalition as well as the head of the Congressional Black Caucus. Levin also has four committee chairs in his favor.

Whichever Democrat wins the primary will be heavily favored in the general election; President Joe Biden won the new 11th District by 20 percentage points.

Battleground Democrats are particularly irked by Levin’s choice to vie against Stevens, saying that they saw it as a kind of political duty for him to run in the tougher 10th District. His decision to challenge a colleague not only means the party is facing tougher odds to hold the seat, it also means more resources spent against fellow Democrats as they struggle to hold the House.

Rep. Cindy Axne (D-Iowa), who faces another tough reelection fight this fall, made a similar case to Levin on the House floor recently — an exchange that multiple people who observed it described as tense.

People who witnessed the exchange described it this way: Axne called out Levin for running Facebook ads that urged donations to his campaign to help save the House.

If he cared about protecting the majority, Axne added, he would have run in the 10th District.

Nicholas Wu and Ally Mutnick contributed to this report.