“The truth is there’s a quiet civil war going on in the Democratic Party right now,” Andrew Cuomo told Fox News, as he fought for his political life against rival Zohran Mamdani a week out from the New York City mayoral election. “You have an extreme left. Radical left. Bernie Sanders, AOC [Alexandria Ocasio-Cortez] — Mamdani is just the banner carrier for that movement — versus the mainstream moderate Democrats.”

“And that’s what this election is about,” he said. “It is that civil war. . . . I believe it will destroy the Democratic Party nationwide, if that far left becomes dominant. This is not a socialist country.”

The United States is not a socialist country. But its biggest and wealthiest city — the heart of its powerful financial sector, where the second-most billionaires in the country reside, and where one in twenty-four residents are millionaires — did just enthusiastically elect a socialist as its mayor, giving him a majority of the vote in a three-way race and a 9 point winning margin.

Mamdani ran up wide margins, sometimes double-digit ones, against the disgraced Cuomo in all of the city’s boroughs but one. New York was the only place last night where voters were not largely driven by wanting to vote against something, namely the president, a stark reversal from Democratic politics as usual in the Trump era, where the party’s lack of an affirmative agenda has seen anti-Trump animus serve as its leading motivator.

Mamdani’s win may be the Left’s biggest victory so far in the civil war that Cuomo described — a war that started in earnest ten years ago, when Sanders threw his hat in the ring for the Democratic nomination and found to even his and his supporters’ shock that a surprising amount of the country wanted to buy what he was selling. Since then, that war has been full of stinging defeats for the movement Sanders inspired, not least of which was the Vermont senator’s own 2020 run, which began with the unprecedented milestone of winning the first three Democratic primaries, before the equally unprecedented milestone of being crushed in almost every single one that followed.

Yet a funny thing has happened after Sanders’s 2020 loss sent many on the Left into a spiral of despondency: socialists kept on winning.

They kept winning, in fact, in spite of regular pronouncements that this or that result finally spelled the Left’s defeat and irrelevance and proved centrists’ firm hold over the Democratic Party. It wasn’t merely wishful thinking: a string of demoralizing losses after 2020 really did happen, whether Eric Adams’s mayoral victory, the two-time defeat of former Sanders ally Nina Turner, or, maybe most bitter, India Walton’s shock loss in Buffalo, so traumatizing that many Mamdani supporters last night refused to believe the prospect of his victory until it was officially announced.

Yet in the midst of these setbacks, the socialist movement continued to more quietly rack up victories and build up its ranks in elected office, even as it escaped notice by many political observers. Though socialists who hold any kind of position of power in the United States are still small in number, they were expanding their influence long before Mamdani delivered Cuomo two well-deserved national humiliations.

There are now more than 250 Democratic Socialists of America (DSA) members holding office across forty states, 90 percent of them elected after 2019, and occupying positions in everything from city councils and county boards to state legislatures and the US Congress. There, the left-wing Squa” now has, depending on who you ask, as many as nine members in the House. At least four of them, like Mamdani, came out of or are former members of DSA, with two more who held two terms each before being ousted in 2024.

In some places, like Minneapolis and Portland, Oregon, socialists have helped form progressive majorities on city councils. Socialist officeholders have played a leading role in major progressive achievements in these places, whether Minneapolis’s establishment of minimum pay for rideshare drivers, Chicago’s elimination of the sub-minimum wage for tipped workers, or, especially, New York’s spate of tenant protection laws and its landmark 2023 decarbonization law.

Where former Democratic president Barack Obama once had to strenuously deny the accusation that he was a socialist who wanted to “spread the wealth around,” openly socialist politicians like Ocasio-Cortez who make a virtue of this very promise are now the leaders of the Democratic resistance to Trump’s agenda. Democratic voters say they prefer socialist politicians to the corporate centrists that currently run the party by 20 points and think their party’s economic policies should have more socialism rather than more capitalism by 12 points, and even 17 percent of independents consider themselves democratic socialists, about the same share (18 percent) that think of themselves as part of the MAGA movement.

In other words, the fear Cuomo expressed on Fox — that his corporate-friendly, neoliberal wing was being eclipsed within the Democratic Party by Sanders’s movement — was already being realized well before last night’s result.

Mamdani’s win is the latest and arguably most important victory in that “war.” Technically socialists have already won much higher-ranked offices: the Senate seat Sanders has occupied for nearly two decades, for instance, or the House seats taken by the Squad, one of which, AOC’s, involved ending the career of a man considered a future House Speaker.

But none have had the kind of money thrown at them like Mamdani’s opposition threw into the New York mayor’s race. The more than $36 million that Mamdani’s opponents alone spent during the mayoral primary race far surpassed the total spending in the single most expensive House primary race in US history: the American Israel Public Affairs Committee (AIPAC)–backed challenge that removed socialist Jamaal Bowman from office last year.

And none have weathered the kind of sustained national attention, scrutiny, and vitriol that Mamdani’s campaign had to to wrench the candidate from dead last in a crowded field to mayor-elect who won with a majority. And it is easily the highest executive position won by any socialist candidate so far, putting Mamdani directly in charge of governing a massive, unwieldy city of 8.5 million and an economy bigger than that of all but eleven whole countries.

The Democratic establishment only has itself to blame for this. Mamdani’s victory over Cuomo doesn’t happen in a world where the Democratic Party doesn’t close ranks around failing (and in Joe Biden’s case, manifestly unfit) politicians, repeatedly handing power to Trump — let alone one where they don’t stubbornly support a two-year-long Israeli genocide that most Americans are disgusted by. Just as they had with Trump, the Democrats successfully staved off the Left, only to quickly squander their own victory, to the point that the party is now disliked by nearly two-thirds of its own voters.

This failure has effectively created a wide open lane for democratic socialists and workers’ movements to accelerate their efforts to supplant the party’s literally decaying establishment. We can see a version of what’s happened in New York now happening all over the country: in the rise of several outsider populists who are catching fire in primary races, like Michigan’s Abdul El-Sayed; in labor-backed populist Dan Osborn’s decision to reject the state’s Democratic Party and be politically rewarded for it; and, most clearly, in Maine voters’ current refusal to abandon left insurgent Graham Platner after what looks to have been a smear campaign meant to clear the way for an establishment alternative.

In many ways, it’s a mirror image of the transformation that the Republican Party itself went through in the back half of the twentieth century, when conservative activists frustrated at what they called the GOP establishment’s support for a “dime-store New Deal” fueled a multi-decade-long effort to take control of the Republican Party and tilt both it and national politics firmly to the right. That successful effort similarly happened in fits and starts, a combination of grassroots organizing and electoral campaigns like primary challenges that saw big, high-profile victories peppered with lots of bitter defeats.

Many voices on the Left have argued that the myriad legal obstacles put in place by the party duopoly that hamper the emergence of third parties make winning control of the Democratic Party an unavoidable, practical necessity. Mamdani’s win will likely be a major boost to their case.

To be clear, that isn’t what has happened as of last night, despite both what Cuomo fears and what Mamdani’s supporters might fervently hope. The Democratic establishment is still the Democratic establishment. But Mamdani’s win last night is a powerful rebuke of that establishment, of the Democrats’ House leader who begrudgingly endorsed him when he had no other choice, of the party’s Senate leader who steadfastly refused to do so, and of the head of one of its chief fundraising arms who took the time to openly smear him.

Democratic voters have lost faith in this leadership, which has long been out of touch with them on policy but has now also proven serially unable to deliver on the one thing it did promise them: to stop Trumpism. It’s hard now to imagine party leaders today maneuvering to stop a well-organized insurgent challenge in its tracks as they did with Sanders in 2016 and 2020 — in fact, their impotence in the face of Mamdani’s rise is proof they can’t.

Defeating this fossilized establishment has, unfortunately, always been the necessary precondition to mount an actually effective challenge to a rising far right. Mamdani’s win will serve as a shot in the arm for similar efforts around the country looking to make that happen, just as it will provide inspiration to the millions around the world keeping a laser eye on this race, desperate for some — any — sign of a hope in a world that seems to be sliding in only one, increasingly grim direction.

In reality, things were never quite as hopeless as they felt. But what may set Mamdani’s win apart from the previous few years of more modest socialist wins is not just that it happened, but that it has imbued a movement built on the hope for a better world with a renewed sense that it’s not just fooling itself. That’s a victory bigger than any one election.