Talk of popular control of the means of production is anathema to many older Democrats, even very liberal ones. It plays a lot better with the young; one recent survey shows that 61 percent of Democrats between 18 and 34 view socialism positively. The combination of the Great Recession, the rising cost of education, the unreliability of health insurance and the growing precariousness of the workplace has left young people with gnawing material insecurity. They have no memory of the widespread failure of Communism, but the failures of capitalism are all around them.

The D.S.A. alone neither claims nor deserves sole credit for the victories of candidates it endorses. Many groups came together behind Ocasio-Cortez, including the populist Brand New Congress and local chapters of the resistance group Indivisible. Nor was the D.S.A. the prime mover behind the Fiedler, Lee and Innamorato wins, though it helped in all of them.

Indeed, while there’s a lot of talk about an ideological civil war among Democrats, on the ground, boundaries seem more fluid. In Pennsylvania recently, I met with moderate suburban resistance activists who’d volunteered for Innamorato, thrilled to support a young woman who could help revitalize the Democratic Party.

Barry Rush is a 63-year-old retiree who used to vote for both Democrats and Republicans, but who, horrified by Trump, now devotes himself full time to a liberal group called Progress PA. His main concern is electing Democrats — “I’m gonna pull the Smurf lever till this gets fixed,” he says of voting blue — and he knows that the Democratic Party needs young people. He was heartened by all the millennials at Innamorato’s victory celebration: “There were 500 kids there!” he said. It gave him hope for his grandkids.

The young members of the D.S.A., meanwhile, are hopeful because their analysis helps them make sense of the Trump catastrophe. They often seem less panicked about what is happening in America right now than liberals are, because they believe they know why our society is coming undone, and how it can be rebuilt.

“The Trump disaster is that everyone feels threatened individually, and feels like they have to fight Trump and fight this administration,” Arielle Cohen, the Pittsburgh D.S.A.’s 29-year-old co-chair, told me as I sat with her and two other chapter leaders in a small coffee shop in the city’s East End. “And socialists are saying, this has actually been going on for a long time. It’s not just Trump. It’s not just who’s in office.”

There is a strange sort of comfort in this perspective; the socialists see themselves as building the world they want to live in decades in the future rather than just scrambling to avert catastrophe in the present.