Zohran Mamdani’s shock victory in this year’s New York City Democratic mayoral primary upended New York politics and called into question the effectiveness of big local unions, which mostly lined up behind loser Andrew Cuomo.

But labor was far from unified behind Cuomo: some unions opposed him, and one major union, the United Auto Workers (UAW), was the first to endorse Mamdani last fall.

This endorsement came at a time when Mamdani was a relatively unknown state legislator. It was the result of rank-and-file activism and a new culture of openness, transparency, and progressivism in the UAW.