It was hard to miss the civic spirit spilling out of Zohran Mamdani's New York City mayoral campaign. You could find his canvassers gathering at parks, playgrounds, and plazas; at 5:30 pm on weekdays or noon on weekends; huddled under the awnings of Dunkin' Donuts or lingering outside independent coffee shops; and in groups as small as pairs and as large as 150.