Standing in the lobby of the art deco theater where Zohran Mamdani held a raucous rally last week, just hours after Israeli hostages were freed by Hamas in a ceasefire deal, the organizer was dressed the part: A black T-shirt with the phrase “Land Back” on the top of a circle, “Democratic Socialists of America” on the bottom, a Palestinian flag in the middle.

The pitch was the same to each prospect he sidled up to: “You look like you might want to sign up with the DSA.”

Mamdani’s emergence is the biggest electoral achievement the DSA has ever had, well beyond the scattered state legislature and city council seats flipped their way in recent years, or even Alexandria Ocasio-Cortez going from being a one-time bartender to a potential top presidential contender. Here in Mamdani was a candidate who’d been a regular of their conventions and organizing Zoom calls, toppling an opponent in Andrew Cuomo as proud of his standing with the establishment as his own famous last name.

Amid a larger bipartisan pull toward populism and mounting anger toward corporations and billionaires, DSA members tell CNN their meetings around the country are attracting more people than ever. Socialist chapters in cities have turned mass Signal chats into de facto National Guard and ICE monitoring groups, and affiliated candidates build up volunteer lists and fundraising beyond anything they’ve seen to date.

Alexandria Ocasio Cortez at a "Fight Oligachy" rally in Denver, Colorado on March 21. Chet Strange/Getty Images

They insist that moderate Democrats panicking and Republicans salivating over pinning their ideas to progressives at large ha