Zohran Mamdani’s victory in the New York City mayoral election leaves the US left in uncharted territory. Though democratic socialists have won a series of national races in the decade since Bernie Sanders’s 2016 presidential run, nowhere has a left-wing candidate had the opportunity to wield such meaningful executive power.

With few recent precedents to draw on, Mamdani has invoked Milwaukee’s twentieth-century “sewer socialists” as a reference for how he will approach governing, while others have looked to draw relevant lessons from the Paris Commune and interwar Red Vienna. Yet a far more immediate parallel for understanding the challenges awaiting Mamdani when he takes office in January is the Spanish left’s experience after 2015 of governing two of Europe’s largest cities.

Swept to office on the back of the indignados wave of anti-austerity protests, and with the backing of left populist Podemos, mayors Ada Colau in Barcelona and Manuela Carmena in Madrid set out to curb housing speculation, rebuild public services, and democratize city institutions. Like Mamdani’s mayoral run, their insurgent campaigns created an air of generational change as they united broad electoral coalitions of younger, middle-class voters hit by austerity, working-class communities, and center-left tactical voters to defeat establishment incumbents.