Zohran Mamdani has won a decisive victory in the primary race to become the Democratic candidate for the next mayor of New York City, according to The Associated Press, after building a commanding lead in first-choice results that shook the national political establishment.

Mr. Mamdani roundly defeated Andrew M. Cuomo in the Democratic contest, widening his primary-night lead by a significant margin once ranked-choice tabulations were run.

Mamdani, a democratic socialist, added to his margin of victory over former Gov. Andrew Cuomo after the ranked-choice votes were redistributed.