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.

On Tuesday evening, the 33-year-old marked his stunning political ascension when he declared victory in the Democratic primary from a Queens rooftop bar after former New York Gov. Andrew Cuomo conceded.