Success breeds failure. Policies and practices well suited to society at one juncture in history are often poorly suited to the world they have beneficially transformed. If you carry a good thing too far, it can turn out not to be a good thing.

Case in point, one of the most successful public policies in U.S. history, the World War II G.I. Bill, which financed college educations for military veterans. Signed by former President Franklin Roosevelt, it embodied New Deal generosity even as its chief backers included the racist Democratic Mississippi Rep. John Rankin and the supposedly reactionary American Legion. One secret of its success, like that of Social Security, was apparent reciprocity: It provided benefits for those who made some contribution.

In doing so, it subsidized economic and intellectual upward mobility for those from modest or even subsistence beginnings — the children of Appalachian coal miners, eastern and southern European immigrants, and even many Black Americans whose service was limited to segregated units.

This success embedded in the minds of elites and many ordinary Americans the notion that any further expansion of higher education would be good for individuals and the country. State legislatures founded new systems of universities and community colleges. Congress pumped large sums into higher education.

As a result, the share of Americans pursuing higher education rose from just 5% before WWII to nearly two-thirds today, with almost 40% earning a bachelor’s degree.

As Charles Murray argued in his 2008 book “Real Education,” these are far higher percentages than the share of the population with the cognitive skills needed to profit from serious four-year undergraduate study, much less advanced graduate school. Schools have responded with reduced rigor and grade inflation.

The result is that American society, which before the G.I. Bill tended to provide higher education to too few, now provides it to too many. Consequently, we have what the maverick scholar Peter Turchin called an “overproduction of elites.”

One consequence is that the economic premium from a bachelor’s degree is becoming smaller, if not vanishing. Another is that there is a glut of college graduates entering the labor market while the number of those without such a degree is declining.

The result, as Silicon Valley investor Peter Thiel predicted in 2020, is a crash in expectations.

All of which helps explain the election of the self-proclaimed democratic socialist Zohran Mamdani as the next mayor of New York City. His core constituency was “a group that has become increasingly central to American politics,” John Carney wrote in the New York Post.

As Gregory Conti said in an interview with The Economic Times, his core constituency was “the college-educated, cash-strapped professional middle class.”

Nationally, this is a splinter group. Mamdani got just 50.4% of the vote in a city where the last four Democratic presidential nominees got 68%, 76%, 79% and 81%. But the command of police forces in central cities with a disproportionate share of the nation’s economic product and violent crimes has consequences.

Surveys show that Mamdani received high percentages from recent migrants to New York and from young voters. Neither has memories of how the crimefighting policies of former Mayors Rudy Giuliani and Michael Bloomberg made the city, and in particular their gentrified neighborhoods, more liberal.

Nor have they experienced the repeated failures of rent control and socialist provision, which Mamdani has championed. The overproduced elite is well positioned to inflict major damage it disdains but feels entitled to lead.