He won by making good on promises. One example: A few years after Mr. Sanders left Burlington’s city hall, the mayor’s office was occupied by a Republican, who cut back the budget for snowplowing, then ran afoul of a heavy winter snowfall. In the next election, remembers the University of Vermont sociologist Thomas Streeter, a bumper sticker read: “At least the hippies plowed the streets.”

That is the secret of Mr. Sanders’s style of politics, once called “municipal socialism.” It’s the ’60s reformist impulse without countercultural baggage. It’s the kind of square that needed time to become hip. It’s a moralistic politics that takes seriously the democratic proposition that elected officials must deliver results.

“The fact that he wins elections says there’s an alternative to Clinton-style politics,” says Mr. Streeter, referring to the reliance in the 1990s on conservative budget-balancing. It was precisely that sort of alternative Lee Webb and others promoted in the 1970s, with the Vietnam War over and the former New Left at sea.