Mark Kingwell is a professor of philosophy at the University of Toronto.

You might think that Rudy Giuliani’s latest tire-fire television interview was just another stop on the highway of craziness down which he is lately barrelling. Sadly desperate for a job close to power, Mr. Giuliani has proven that some people who work for Donald Trump are even more unhinged than the President himself.

Mr. Giuliani has lost all contact with reality as most of us experience it, such that he can weave webs of nonsensical verbiage that he appears to believe. Asked to explain how the Mueller investigation could possibly create a “perjury trap” for Mr. Trump, Mr. Giuliani argued that the background presumption of truth in inquiry, even if you answer questions honestly, is not in fact true. “Truth isn’t truth,” he said.

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As many people pointed out, Mr. Giuliani contradicted himself with this now-notorious apothegm. Is it true that truth isn’t truth? You just said so! But doesn’t that mean there is truth? Or are you lying again, right now? But then, doesn’t that mean there is truth after all?

I’m pretty sure Mr. Giuliani didn’t mean to indulge in philosophical paradox here, given that he shills for the current global Master of Mendacity. We know the current notion of truth in Washington: When I’m talking, it’s true. When anyone else is talking, it’s not true – unless I agree with it. Mr. Trump and his minions are now so adept at this move that I bet they can’t tell the difference any more. Paul Manafort (convicted felon) is a good guy! Michael Cohen (self-admitted federal criminal) paid people off because he likes to! Also, he is a liar!

I could go on, but pretty soon my head would explode. But this isn’t merely another alternative-fact moment in the contemporary world of right-wing post-truth postmodernism, where nothing is ever really true if you deny it loudly enough. In a sentence I never thought I would write, Mr. Giuliani is Pontius Pilate, oozing skepticism about the very idea of truth. Unlike the cynical prefect, he lacks the wit to leave the room – or the interview chair – promptly.

Worse, and inspired by Mr. Trump’s example, populist political fudging is becoming more widespread and more disastrous. An exasperated editorial in The Guardian put it this way: “Rightwing populism does not ‘do’ complexity. Experts are scorned, conspiracy theories involving malevolent outsiders are embraced. Policy is for nerds. Its political mouthpieces cannot countenance nuance, let alone failure. They are asked for, and provide, immediate gut answers – which are almost invariably wrong.”

That was written before Mr. Giuliani’s administration-defining phrase was uttered, but his TV-show babble neatly summarizes Mr. Trump’s evasion-enabling, base-supported reality-denial. Consider, then, that just recently in Italy (bridge collapse), Turkey (currency devaluation), India (flood emergency) and the United States (too many to mention), stark failures of foresight, infrastructure, emergency planning and economic theory have destroyed actual lives – not just juggled philosophical concepts. These failures of leadership are demonstrably linked to the self-serving populist rhetoric of their dominant politicians. Once you start to lie comprehensively, there is every reason to begin dodging every kind of accountability levelled at you by fact-checkers, reporters, unco-operative investigators, and all the other people who actually see what you are up to.

There are, of course, excellent reasons for sometimes doubting someone’s claim to truth. Ironically, they include a lot of the features observable in the very people who now disdain truth altogether: relentless personal animosity, non-transparent financial interests, narcissism, hubris, and the kind of blithe perversity that results when people never contradict you – or you fire them when they do. Doubting a given truth-claim is how we get better at truth, not a reason to say there is no truth.

One benefit of Mr. Giuliani’s inability to parse the logic of his own inane bluster is that, despite appearances, it’s not actually nonsense. That is, it has a weird semantic weight that defines the series of impeachable moments of the past week. Former admiral William McRaven, in the wake of Mr. Trump’s unprecedented removal of security clearances, wrote a version of this sad truth: “Through your actions, you have embarrassed us in the eyes of our children, humiliated us on the world stage and, worst of all, divided us as a nation.”

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We all know Mr. Trump is shameless. Far worse is the fact that his remaining supporters remain so shameful. Truth will out.