Take heed, New Yorkers, and learn from San Francisco’s mistakes: The City by the Bay has discovered to its sorrow that charismatic leaders like Zohran Mamdani can dazzle — but their decisions can be disastrous. Just a few years ago San Franciscans, too, supported magnetic populists, then watched as their neighborhoods fell off a livability cliff. Regrets, we have more than a few — and many we want to mention. In 2017 London Breed, a brash and captivating city supervisor from the projects, became acting mayor when the mild-mannered Mayor Ed Lee died. With big promises of housing creation, downtown...