The rise of Zohran Mamdani does not mark a new turn in city policy so much as it reflects a rejection of reality.

Political candidates can be forgiven for making sensational promises in their quest to win office, but the number of people willing to suspend disbelief is a barometer of our politics.

And the current reading is troubling.

For the better part of a century, the city’s political progressives (once called “liberals”) argued about how big a slice government should take from the private sector to serve public purposes, and the extent to which government should regulate private transactions.

Left unsaid is the recognition that private markets, and market actors, were the source of whatever piece they’d take in taxes for schools, police and public uses.

Mamdani, born two years after the Berlin Wall fell, rejects that premise.

He goes beyond just offering to have government tax more to pay for things — buses, college, childcare.

He challenges the very idea of private ownership, most notably in the housing market, where he’d look to strangle building owners with a four-year rent freeze.

Think landlords will eat the loss forever?

In the 1970s, they abandoned thousands of money-losing buildings, contributing to the city’s grim decline.

Mamdani’s plans to finance his agenda likewise fail to face reality.

He’d need state permission for massive tax increases, which would only cover a fraction of his proposed spending.

Even more impractically, he’s counting on these new revenues flowing to city coffers without interference from 213 state lawmakers or the governor.

Mamdani and his followers ignore the poor track record of government-owned ventures: the horror stories endured by NYCHA tenants, the mediocre outcomes in city-run schools, the struggles to operate, let alone expand or improve, the city’s mass transit.

To Mamdani, these are mere details — red herrings, even, flung by greedy capitalists.

Data and evidence don’t matter to the 33-year-old with only four years’ experience as a lawmaker.

He’s part of a populist movement that disregards both.

In some ways, he embodies a dynamic playing out on the other end of the political spectrum, where DC Republicans are breathlessly defending unsustainable deficit-spending that will eventually push the nation into a debt crisis.

Both approaches — pretending debts or markets don’t matter — will end in ruin.

If Mamdani prevails in November, it will be up to his fellow Democrats in Albany to tap the brakes on plans that could measurably damage the economic standing of the city, and with it, the state.

In some cases, they need only do nothing: they can reduce the risk of business and high-earner outmigration by leaving city tax rates where they are.

In other cases, they might have to act, especially if and when Mamdani’s anti-landlord stance translates into more vacant apartments becoming uneconomical to renovate, or if his posture toward police erodes public safety.

Either way, Albany is counting on stability in the five boroughs to keep cash coming into state coffers, among other things.

Nothing about New York City’s weather or geography makes it the natural permanent seat of global commerce.

Its political climate risks changing that.

Ken Girardin writes about New York public policy. All opinions expressed are his own and not the views of his employer.