Mamdani’s mother, Mira Nair, is an award-winning filmmaker whose credits include “Monsoon Wedding,” “The Namesake” and “Mississippi Masala.” His father, Mahmood Mamdani, is an anthropology professor at Columbia University.

But whatever happens in November, Mamdani already has earned the most support of any U.S. politician who endorses the movement to boycott Israel. His victory offers a clear sign that backing the movement, known as BDS, is hardly the red line that its critics long tried to make it.