For history buffs, Mr. Mamdani has done the service of rekindling an interest in a largely forgotten American tradition, the “sewer socialists” who ran a significant list of cities in the last century. The most durable among them was Daniel Hoan, the socialist mayor of Milwaukee from 1916 to 1940. You don’t get reelected that often by being a failure.

Many socialist mayors did not mind being associated with repairing the grubbiest of urban amenities because doing so underscored their aim of running corruption-free governments that did whatever they could to improve the lives of working-class people in their jurisdictions. When lousy (or nonexistent) sewer systems led to illness and death in low-income and immigrant neighborhoods, said Michael Kazin, a historian at Georgetown University, building and fixing sewers became a powerful example of what “common good” governance could accomplish.