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.

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.