The new demographics have hollowed out the political middle in most cities.

The old urban middle class leaned Democratic, but they were largely interested in practical outcomes — like paved roads, fixed lights, and access to jobs. Their departure, and replacement by temporary hipster populations, has helped insulate city governments from constituents who would be most adamant about reforming usually failed school districts or demanding improvements in public infrastructure or maintaining public order.

Electoral engagement has faded in most cities, with turnout for mayor averaging 15 percent for mayoral races in our most populous cities. In Los Angeles, the 2013 turnout that elected progressive Eric Garcetti was roughly one-third of that in the city’s 1970 mayoral election. Garcetti’s 2017 re-election boasted a similarly low turnout.

The prime beneficiaries of these changes have been the well-organized. Rep. Alexandria Ocasio Cortez’s primary victory rested on 16,000 votes out of a total Democratic registration of almost 215,000. She won not by sweeping the proletarian or minority masses, but marshalling the votes of white young educated hipsters. These voters are driving the rise of far-left socialists in other cities, including Denver, who seek to replace not Republicans but more traditional liberal Democrats.