Everybody is talking about Zohran Mamdani, the state legislator and New York City Democratic mayoral nominee who has become a national news story. But not everyone understands why Mamdani has captured so much attention.

Mr. Mamdani’s victory upended city politics and reverberated nationally. He relied on a memorable message, charisma and a strong ground game.

As food costs climb and public trust in private solutions falters, a government-supported grocery model is moving from fringe idea to policy experiment.