US, June 26 -- NYC Mayor Zohran Mamdani was not on the ballot in New York's Democratic congressional primaries. Yet by the end of the night, the city's mayor had emerged as their most consequential winner. All three candidates backed by Mamdani won their races.

Brad Lander defeated sitting Congressman Dan Goldman. Claire Valdez beat Brooklyn borough president Antonio Reynoso for an open House seat. Darializa Avila Chevalier pulled off the night's biggest upset by unseating veteran Congressman Adriano Espaillat.

The results gave Mamdani a clean sweep and strengthened the argument that his surprise victory over Andrew Cuomo in last year's Democratic mayoral primary was not an isolated political shock. His campaign organization, endorseme...