Maine Governor Janet Mills’s decision to suspend her U.S. Senate campaign and effectively concede to upstart Graham Platner is a huge temporary victory for progressive Democrats in their ongoing fight with the party’s center-left establishment wing. But it will only be a true victory for progressives if Planter wins in November. And the left will be diminished if the untested Platner loses the general election because of baggage from his past or political inexperience—the unknowns that left many party insiders preferring Mills. The media, the parties, activists, and even average voters across the country have been captivated by Mills vs. Platner in part because the Maine election is one of the most important contests of this year’s midterms. Democrats must flip four seats this November to gain control of the Senate. Maine is their most obvious target because incumbent Susan Collins is the only Senate Republican up for reelection in a state Kamala Harris carried in 2024. There is almost no path for a Democratic Senate majority that doesn’t involve the Pine Tree State. But this race is also a proxy for broader tensions within the Democratic Party. Mills is a 78-year-old in a party where many voters blame the American authoritarianism of the last year on an 80-something president who insisted on running for reelection despite bad poll numbers and diminished faculties. She was recruited into the race by Senate Minority Leader Chuck Schumer and endorsed by a broader party establishment that younger, more progressive Democrats think is weak and ineffective. She doesn’t take many bold policy positions. In contrast, Platner has taken left-wing stances on most hot-button issues. He’s endorsed by Senators Elizabeth Warren and Bernie Sanders and advised by some of the consultants who worked for New York City Mayor Zorhan Mamdani. Some Democrats think his service in the Marines, his working-class job as an oyster farmer, and other personal attributes are the way for the party to connect with white men without college degrees. Other Democrats think elevating Platner is the latest sign of a party doing ham-fisted and ineffective pandering to white men. Once Mills started her campaign in October, with Platner already in the race, this primary became another fight in the war between progressives and moderates both in Maine and nationally. But Platner didn’t outpace her simply on the merits of his ideological arguments. In the latest edition of Right Now, the TNR show I host, Midcoast Villager deputy editor Alex Seitz-Wald said that Platner surged ahead of Mills in the polls in part because he was out-hustling her, holding far more campaign events than the governor. But these national themes were factors, as well, according to Seitz-Wald. Mills was dogged by criticisms that Democrats shouldn’t give a major role to another person in their upper seventies and that she would largely align with the party establishment in Washington. Polls showed Platner with a massive lead among voters under age 35, the bloc most hostile to the establishment and supportive of progressives. Seitz-Wald argued that Mills’s veto last week of a proposed moratorium on the construction of data centers in Maine was the final nail in the coffin for her campaign. That move deeply irritated Democratic activists. And artificial intelligence, which is driving the boom in data centers, is another issue entangled in the party’s center-versus-left tensions, as Sanders has been a leading proponent of greater AI restrictions. Mills, in her statement on leaving the race, said that she was dropping out because of a lack of money. It’s true that Platner had raised far more than her. But I suspect Mills also saw the prospect of her political career ending with a 20 or more percentage point primary defeat and decided to spare herself that embarrassment.Now comes the real test for Platner and progressives. They argued that Platner is as strong a candidate for the general election against Collins as Mills would have been. That’s a very controversial claim, considering that Mills was twice elected governor of this state. It’s an even more controversial claim since Platner spent months last fall apologizing for sexist and racist things he wrote on message boards in his pre-political career and a tattoo that included a Nazi symbol. The left’s theory is that voters these days are looking for relatable people with normal lives (including faults) instead of career politicians. I’m not sure. Yes, Donald Trump is president, but Democrats are well positioned for Senate races in Alaska and North Carolina because they have battle-tested politicians running in those states. Mills might have lost to Collins anyway. But she would have lost for normal reasons. Platner introduces a whole host of unknowns. Democrats have nominated more traditional candidates against Collins before, and she has defeated them. I don’t think there is anything wrong with trying a different approach this year. But for progressives, Platner is a big bet. He wins in November, and it’s harder for the Democratic Party to dismiss outsider candidates with progressive views in key Senate races and even for president. He loses, and centrist Democrats will claim that the party would have won a Senate majority if the left hadn’t insisted on pushing a political neophyte with a Nazi tattoo. Either way, what happens in Maine won’t stay in Maine.