While Democrats across the country are pulling their hair out over Michigan's brutal Democratic Senate primary, a key House race in the state is also quietly giving party leaders heartburn.Why it matters: Infighting between establishment Democrats could create an opening for a progressive who many Democratic strategists and lawmakers are skeptical can win the seat in November.Moderate Democrats and party leaders' inability to coalesce behind a single candidate has become the source of considerable behind-the-scenes acrimony, Axios has learned."This has gotten really intense," said a senior House Democrat, who, like others quoted in this piece, spoke on the condition of anonymity to offer candid analysis on the race and the anger surrounding it."It's a serious clusterfck," a Michigan state legislator told Axios. "I am just sitting back eating popcorn because now it's so fcked up it's just, 'Let's just enjoy this.'"State of play: Three Democrats are running in the primary to take on Rep. Tom Barrett (R-Mich.) in Michigan's 7th district, which President Trump won by just over a single percentage point in 2024.Bridget Brink: A career foreign service officer who resigned as ambassador to Ukraine last year over Trump administration policy, backed by the Democratic Women's Caucus.William Lawrence: A co-founder of the progressive climate organization Sunrise Movement, endorsed by the Congressional Progressive Caucus and Sen. Bernie Sanders (I-Vt.).Matt Maasdam: A retired Navy SEAL and military aide to former President Obama supported by Sen. Elissa Slotkin (D-Mich.).What we're hearing: Slotkin, who represented the seat before Barrett, has rankled some colleagues and fellow Michigan Democrats by boosting Maasdam in the final stretch of the campaign.In addition to recruiting Maasdam and then endorsing him and cutting an ad on his behalf last week, Slotkin has lent her name to his fundraising texts and paid for internal polling on his behalf, according to emails and texts viewed by Axios and multiple sources familiar with the matter.A senior House Democrat said the frustration over Slotkin's push for Maasdam ranked some leading Democratic Women's Caucus members, telling Axios: "The Women's [Caucus] went apesht. And I mean apesht."What they're saying: Several Michigan Democrats fumed that Slotkin's support for Maasdam risks eating into the lead that Brink has held for much of the campaign and creating an even larger opening for Lawrence.State Rep. Jennifer Conlin, who described Slotkin as a mentor, told Axios she "found it so perplexing" the senator endorsed Maasdam given that Brink shares her background as a woman in national security."It's just very strange to me that she would be endorsing Matt," Conlin said.Another local elected official expressed confusion at Slotkin's support for Maasdam because, they told Axios, the senator has told local allies "very plainly" that any Democratic nominee in the district "has got to be a woman."The other side: "Senator Slotkin is singularly focused on one thing: flipping her old seat from red back to blue. Her entire goal is to help win back the House and put a real check on President Trump," said Slotkin spokesperson Josh Stewart.Stewart added: "Matt Maasdam is the best candidate to do that."Dianne Byrum, a former minority leader of the Michigan House of Representatives, said in an interview that the criticism of Slotkin for not supporting a fellow woman is "more noise than anything else.""What we should be focused on is bringing out of the primary the strongest candidate to run against Tom Barrett, and I happen to believe that is Matt Maasdam," Byrum told Axios.Zoom out: Centrist Democrats agree that Lawrence should not be the nominee for a key swing seat, pointing to his left-wing positions and his comments in 2024 that Black Democratic leaders "defang the white left."Rep. Hillary Scholten (D-Mich.) told Axios that Lawrence's past comments "speak to a broader lack of judgment, temperament, and leadership that would leave him ill-equipped to lead in Congress. In short, he can't win.""We have a great chance to win the seat if we get the candidate that can win the seat. Will Lawrence is not that candidate," said Rep. Brad Schneider (D-Ill.), the chair of the center-left New Democrat Coalition.Brink and Maasdam "both would be wonderful," he added. "I wish the two of them were not running against each other but running in two different districts."Yes, but: "Every election cycle, we hear the same inauthentic talking points against candidates demanding real change for their communities," said progressive Rep. Delia Ramirez (D-Ill.).She added: "Voters are tired of empty suits reciting talking points from DC consultants or of those beholden to special interests, defending the status quo rather than delivering for the district."Lawrence argued in a statement to Axios that casting him purely in ideological terms ignores the broader appeal of his anti-data center focus."If you don't live in Mid-Michigan, you don't know how angry people are about AI data centers pushing their way into our communities," he said, adding that his message is "reaching voters across the political spectrum."The intrigue: As if the campaigns and their outside backers wailing on each other relentlessly wasn't bad enough for Democrats, now Republicans may be getting in on the action.Brink's campaign and Slotkin allege that Michigan Sunrise PAC — which started running ads against Maasdam over the weekend — is a Republican front group, noting their bank is mainly used by GOP campaigns.Michigan Sunrise PAC and the Republican super PAC Congressional Leadership Fund did not respond to multiple requests for comment."If Democrats care about winning back the House, they should unify around Matt Maasdam with the same energy as the GOP is expending to see him lose," said Stewart.The race was already awash in spending from outside groups supporting all three candidates, including a Congressional Black Caucus-aligned super PAC spending $1 million on ads attacking Lawrence.The largest spender in the race has been VoteVets, a group that works to elect Democratic military veterans to office, which has spent $2 million in support of Maasdam, according to Federal Election Commission filings.The bottom line: Regardless of who wins, this is a primary that Democrats will be happy to wash their hands of after Aug. 4.Said the state legislator who spoke on the condition of anonymity: "I think everybody's sitting back and saying, 'This is a f*cking nightmare.'"