Donald Trump and his political allies have consistently described American cities as zones of decay and disorder populated by minorities — from his 2016 claim that in “our inner cities, African Americans, Hispanics are living in hell because it’s so dangerous” to Sen. Tom Cotton’s recent portrait of an “orgy of violence” that “plunged many American cities into anarchy.” So when Trump saw urban mass protests accompanied by opportunistic looting, he may have expected to benefit from a forceful articulation of the politics of “law and order” like Richard Nixon did more than 50 years ago.

At a rally in Tulsa on Saturday, Trump conjured up the purported violent horrors in the nation’s Democratic-run cities — warning, “The Democrats’ push against our police will drive up crime and drive up costs at levels you’d never believe. Thousands of innocent lives will be lost.”

But this message has largely backfired. Trump’s net approval rating has undergone a sharp dive and prominent military figures denounced his threat to send troops into cities. The Tulsa rally, his first in months, was under attended.

Why did this political strategy fail today when similar moves worked so well in 1968 and for more than 20 years afterward? In large part because it is hard to argue for deploying troops in the streets of cities that have in recent decades become far safer, economically vigorous and socially vibrant.