Barton Swaim is the author of "The Speechwriter: A Brief Education in Politics" and a contributing columnist at The Washington Post.

Republican presidential nominee Donald Trump and Democratic presidential nominee Hillary Clinton shake hands after the presidential debate at Hofstra University in Hempstead, N.Y., Monday, Sept. 26, 2016. (AP Photo/David Goldman)

An earlier version of this post incorrectly said Donald Trump pressed Hillary Clinton on her contradictory statements about the North American Free Trade Agreement. He was referring to the Trans-Pacific Partnership. This post has been updated.

Donald Trump and Hillary Clinton have very different but similarly complicated relationships with the truth. Trump treats the truth with contempt, Clinton with a feigned politeness. But these two modes of expression are nothing like each other. They are opposites, which is what made Monday night’s debate so revealing.

Clinton’s overriding aim in her public discourse is to avoid outright falsehood. She seems mainly intent not on telling the truth but on not saying anything obviously untrue. Clinton holds a traditional view of truth as something objectively knowable, and nearly all her utterances are calculated to avoid contradicting it. That’s not to say she has a high regard for the truth. It means simply that, in deceiving, Clinton acknowledges the truth as the criterion with which one must deal.

Trump’s aim is the opposite one. He is intent on subverting the truth, or what the political establishment calls the “truth,” as often and as brashly as he can. If he senses that most respected politicians and journalists regard something as true, he will attempt to contradict it. He doesn’t do this because he actually disagrees with whatever conventional truth he’s upending; he does it to signal his contempt for the power structure as it has come to exist in Washington and the news media.

What we witnessed on stage at Hofstra University, then, wasn’t just a debate between two presidential candidates. It was a debate between modernism and postmodernism.

Intellectual historians refer to the period from 1600 to 1945 (more or less) as the “modern” period. It’s always risky to generalize, but truth in the modern era was something objective and knowable, and knowable through material and scientific means (thus not through divine revelation). During the second half of the twentieth century, however, that view of truth was undermined in various ways. Poststructuralism in philosophy, abstraction in art, twelve-tone serialism in music, absurdist fiction in literature — all these things, variously categorized as “postmodernism,” posed direct challenges to the older “modern” view of truth.

I don’t think it’s too much of a stretch to say Hillary Clinton is essentially “modern” in her outlook and approach. She is a cagey politician who isn’t above the use of half-truths and weaselly word-level justifications to further her political ends. But for her, the truth is always there, even if it’s something to avoid facing or dance around or ignore altogether.

Donald Trump is our first full-on “postmodern” presidential candidate. Truth, for him, isn’t some unseen objective entity a responsible politician should refrain from crossing. If there is such a thing, “truth” is only rhetorical or rooted in perspective. The only important “truth” in Trump’s worldview is that the nation’s ruling elite consists largely of incompetents, racketeers and hacks, and they have not yet been moved aside and replaced with Donald J. Trump. Whatever he says in the service of that manifestly noble aim isn’t just excusable but good and right. Negotiating the perils of objective truth has nothing to do with it.

I don’t know how viewers will adjudicate Monday night’s debate, but as I watched I couldn’t help feeling Clinton’s modern-era version of truth looked feeble and helpless in the face of Trump’s postmodern onslaught. When Trump pressed Clinton on her contradictory statements about the Trans-Pacific Partnership — she has claimed she opposed it “from the very beginning” — Clinton was left to struggle impotently against the facts. Against the truth.

“You were totally in favor of it,” Trump said. “Then you heard what I was saying, how bad it is, and you said, I can’t win that debate.” Trump’s criticism is characteristically incorrect — Clinton changed her mind on TPP  long before the 2016 campaign — but her weakness in the face of this criticism is significant. “Well, that’s just not accurate,” she said. “I was against it once it was finally negotiated and the terms were laid out. I wrote about that  in — ”

“You called it the gold standard!” Trump interrupted.

Clinton tried to fight back, but she struggled futilely against that self-imposed burden, the truth. “Well, Donald,” she countered, “I know you live in your own reality, but that is not the facts. The facts are — I did say I hoped it would be a good deal, but when it was negotiated…”

Trump does not burden himself in this way. When asked why he was still questioning President Obama’s place of birth as recently as 2015, Trump first pointed a finger at Clinton supporters in the 2008 primary (that’s fair enough), but then claimed that he, Trump, was responsible for forcing Obama to produce his birth certificate. “I was the one that got him to produce the birth certificate. And I think I did a good job.” But of course the certificate was produced in 2011.

As so often during Trump’s 2016 campaign, plain empirical truth simply isn’t an impediment to whatever the candidate wants to say.

Trump’s rage against Washington’s power elite, his belief that today’s leaders are all nincompoops and criminals absolves him of any need to abide by the petty dictates of literal truth. He is the ironic, self-referential embodiment of the newer postmodern conception of truth. He is a joker, a clown, yes, but a strong and determined one — a Nietzschean Übermensch with ludicrous hair and excellent comic timing. Hillary Clinton, with her weak appeals to objective truth — “that’s just not accurate” — is no match.

For two generations or more, American liberals have cheered postmodern attitudes in art, literature, music and philosophy. Now it has entered politics, and it’s time to panic.