Barton Swaim is author of “The Speechwriter: A Brief Education in Politics” and a contributing columnist for The Post.

It’s true that Donald Trump’s support has little to do with policies. It’s not true, however, that those who support him have no rational or cogent reasons for their preference. They are misguided, in my view, but they aren’t stupid, and we flatter ourselves by assuming their preference for Trump is evidence merely of economic forces they don’t understand.

Donald Trump says the United States is too preoccupied with being politically correct. Here's how the presumptive Republican presidential nominee bashes the idea of being too PC. (Peter Stevenson/The Washington Post)

If the Trump supporters I’ve met and know are a fair representation of their outlook, what binds them together is a deep hatred for political correctness. No groundbreaking analysis there: Trump has railed about political correctness many times, and of course he relishes expressing himself in ways that can reasonably be called politically incorrect. He may be a bigot and a scoundrel, the thinking seems to be, but the one thing he isn’t is politically correct. I don’t dismiss that view. PC culture has been the source of jokes and satire for 25 years or more, but it’s no less real for that. Trump’s supporters aren’t wrong to hate it.

But what is it, exactly?

There’s more to political correctness than an obsession with racial and sexual sensitivities, though those are at the root of it. Political correctness, if I could venture my own admittedly rather clinical definition, involves the prohibition of common expressions and habits on the grounds that someone in our pluralistic society may be offended by them. It reduces political life to an array of signs and symbols deemed good or bad according to their tendency either to include or exclude aggrieved or marginalized people from common life.

PC was born of a generous impulse, maybe — it’s good and right to avoid giving offense, when you can. But it has long been a blight and a menace. It obliges us to think constantly about a few topics — topics having mainly to do with racial and sexual identities, but other sorts of identities as well — even as it makes it impossible for us to speak openly and honestly about those same topics. You must consider every facet of life in light of racial sensitivities, sexual politics or some kind of cultural imperialism; but you’d better not talk openly about any of these things unless you’re prepared to negotiate their exquisite complexities and unless you’re up to date on all the latest banned phrases.

Political correctness is an unwritten and constantly changing code of forbidden language and practices, and most Americans sense its unfairness. They sensed it most acutely, I think, over the past few years, when three political controversies coincided in a way that seemed to proscribe all but center-left or progressive interpretations: race relations as a result of the riots over police conduct in Ferguson, Mo., and Baltimore; same-sex marriage as a result of the Supreme Court’s Obergefell v. Hodges decision; and transgender rights after Caitlyn Jenner’s self-revelation and the Obama administration’s executive order regarding public school restrooms. Americans take all sorts of reasonable and conflicting views on all three of these topics, but all three are subjects on which, depending on the nature of their views, many feel a keen reluctance to speak candidly.

That feeling of delegitimation, of not being able to state one’s beliefs without attracting accusations of bigotry and backwardness, isn’t something most Americans will put up with for long. Many of them felt gagged and irritated, and Trump shrewdly named the thing that troubled them: political correctness. A lot of people fell for it. And in falling for it, they made two disastrous mistakes. First, by promoting political incorrectness as a remedy to the taboos they rightly detest, they gave us a man so loathsome as to make those taboos seem almost sensible. In the saddest irony of this deeply strange election year, Trump’s supporters have managed to enhance the credibility of political correctness: Given the choice between political correctness and the bigoted tirades of a dirty old man, I’ll take political correctness.

Second, those who supported Trump on the theory that he’d push back against political correctness failed to understand that you can’t change a culture from the top. Politics doesn’t determine culture; culture determines politics, and transforms it. A president can do as much about political correctness as he can, say, about the hookup culture on college campuses. Or about the use of hard profanity in polite company. Or about the loss of appreciation for poetry. One may deplore each of these things (I deplore all three), but they are not political in nature and so cannot be withstood or even affected by politics.

Political correctness is an insidious presence in American life. That’s true. But resisting it requires the long and patient work of a generation, not the election of a clownish president.