By Paul Krugman – The New York Times.

Last year there were 352 murders in New York City. This was a bit higher than the number in 2014, but far below the 2245 murders that took place in 1990, the city’s worst year. In fact, as measured by the murder rate, New York is now basically as safe as it has ever been, going all the way back to the 19th century.

National crime statistics, and numbers for all violent crimes, paint an only slightly less cheerful picture. And it’s not just a matter of numbers; our big cities look and feel far safer than they did a generation ago, because they are. People of a certain age always have the sense that America isn’t the country they remember from their youth, and in this case they’re right — it has gotten much better.

How, then, was it even possible for Donald Trump to give a speech accepting the Republican nomination whose central premise was that crime is running rampant, and that “I alone” can bring the chaos under control?

Of course, nobody should be surprised to see Mr. Trump confidently asserting things that are flatly untrue, since he does that all the time — and never corrects his falsehoods. Indeed, the big speech repeated some of those golden oldies, like the claim that America is the world’s most highly taxed country (when we are actually near the bottom among advanced economies).

But until now the false claims have been about things ordinary voters can’t check against their own experience. Most people don’t have any sense of how their taxes compare with those paid by Europeans or Canadians, let alone how many jobs have been displaced by Chinese competition. But 58 million tourists visited New York last year; tens of millions more visited other major cities; and of course many of us live in or near those cities, and see them every day. And while there are, as there always were, bad neighborhoods and occasional violent incidents, it’s hard to see how anyone who walks around with open eyes could believe in the blood-soaked dystopian vision Mr. Trump laid out.

Yet there’s no question that many voters — including, almost surely, a majority of white men — will indeed buy into that vision. Why?

One answer is that, according to Gallup, Americans always seem to believe that crime is increasing, even when it is in fact dropping rapidly. Part of this may be the wording of the question: People may have a vague, headline-fueled sense that crime is up this year even while being aware that it’s much lower than it used to be. There may also be some version of the “bad things are happening somewhere else” syndrome we see in consumer surveys, where people are far more positive about their personal situation than they are about the economy as a whole.

Again, however, it’s one thing to have a shaky grasp on crime statistics, but something quite different to accept a nightmare vision of America that conflicts so drastically with everyday experience. So what’s going on?

Well, I do have a hypothesis, namely, that Trump supporters really do feel, with some reason, that the social order they knew is coming apart. It’s not just race, where the country has become both more diverse and less racist (even if it still has a long way to go). It’s also about gender roles — when Mr. Trump talks about making America great again, you can be sure that many of his supporters are imagining a return to the (partly imagined) days of male breadwinners and stay-at-home wives.

Not incidentally, Mike Pence, Mr. Trump’s running mate, used to fulminate about the damage done by working mothers, not to mention penning an outraged attack on Disney in 1999 for featuring a martially-minded heroine in its movie Mulan.

But what are the consequences of these changes in the social order? Back when crime was rising, conservatives insistently drew a connection to social change — that was what the whole early ’90s fuss over “family values” was about. Loose the bonds of traditional society, and chaos would follow.

Then a funny thing happened: Crime plunged instead of continuing to rise. Other indicators also improved dramatically — for example, the teen birthrate has fallen 60 percent since 1991. Instead of societal collapse, we’ve seen what amounts to a mass outbreak of societal health. The truth is that we don’t know exactly why. Hypotheses range from the changing age distribution of the population to reduced lead poisoning; but in any case, the predicted apocalypse notably failed to arrive.

The point, however, is that in the minds of those disturbed by social change, chaos in the streets was supposed to follow, and they are all too willing to believe that it did, in the teeth of the evidence.

The question now is how many such people, people determined to live in a nightmare of their own imagining, there really are. I guess we’ll find out in November.