We now know Trump is proud of his pathological lying. That makes him much more dangerous than we thought

A leaked audio recording of Trump recalling his talks with the Canadian Prime Minister Justin Trudeau at a private fundraising event in Missouri revealed that Trump isn't deluded; he knows what he's doing, and he enjoys it

Donald Trump tells lies. That’s hardly news, of course. And certainly not fake news. According to The Washington Post, which is assiduously keeping count, the 45^th US President has uttered or tweeted more than 2,000 false or misleading statements since swaggering into the White House. That’s an average of around five a day.

But does Trump spew this waterfall of lies knowingly? Or could it be that he is just chronically ignorant and obscenely intellectually lazy? Or is it perhaps a case of cognitive impairment, as suggested in a recent book? Is Trump mentally unable to distinguish between fantasy and reality?

A leaked audio recording of Trump recalling his talks with the Canadian Prime Minister Justin Trudeau at a private fundraising event in Missouri gave us a pretty strong steer on this.

Trump bragged to his audience that he asserted something to the Canadian leader that he simply didn’t know was true or not. “I said, ‘Wrong, Justin, you do [have a trade surplus with the US].’ I didn’t even know ... I had no idea. I just said, ‘You’re wrong.’”

In other words, Trump has admitted that he lies knowingly and shamelessly. Indeed, the Missouri audio demonstrates that he’s not merely shameless, but proud of his untruths.

There are problems with psychological diagnoses from a distance, but it’s worth noting that pathological lying and immunity to feelings of guilt are traits associated with psychopaths.

Is there anything more to be said about Trump’s estrangement from truthfulness?

Yes. And it’s the fact that Trump is a political liar. The lies are not simply intended to deceive; they are, as the Russian dissident Masha Gessen has argued, a brute assertion of the primacy of power over truth, of a conception of power that simply does not recognise the authority of truth.

Trump says something that is untrue, that people around him know is untrue, that he himself knows to be untrue, and which he knows they know is untrue. Why? As a statement of his authority and the absolute nature of it. As the Missouri audio also reveals, the job of his aides, when a lie is told by their master, is to locate some evidence that his assertions are, in fact, correct.

By forcing his spokespeople and subordinates to repeat, defend or rationalise his blatant falsehoods in public, he destroys their own reputations and their own sense of self-respect. This may, or may not, be intended as a means of binding them more closely to him. Although given the rate at which personnel have been departing the Trump administration, it has arguably not been particularly effective in that regard.

Yet there’s ample evidence that Trump is also a calculated and manipulative liar. The timing of his tweets makes it plain that he frequently uses lies to create media frenzies, to distract from other uncomfortable stories, to whip up his voter base. His lies are thus a form of propaganda, of disinformation.

It’s impossible not to summon to mind, writing all this, the repeated insistence of an apparently guilt-free Boris Johnson that the UK sends £350m a week to the European Union’s coffers, even when the UK statistics watchdog has explicitly told him that this totemic Brexiteer claim is simply wrong.

How to cover shameless, political and calculating liars and propagandists such as Trump (and, on dark days, Johnson) represents an immense and complex challenge for the media.

The instinct is to seize on the lie, to “fact check” an individual assertion and demonstrate why it’s wrong. I’ve written plenty of such debunking articles myself of Trump’s various statistical abuses.

Yet if the objective of the lie is to distract, to dictate the news agenda, one can’t get away from the fact that this risks dancing to Trump’s tune.

And what of the impact on the public? Some psychological research hints at a “backfire effect”, where people become more entrenched in their wrong convictions, perhaps fed to them by Trump, when they are exposed to contrary evidence.

The validity of this finding has been contested by other researchers. But nevertheless, it’s pretty clear that truth in America is under the cosh, led by the assaults of its liar-in-chief. Trump’s US support base has not grown since the 2016 election, but it has not collapsed either.

Heartbreaking as it is for liberals to acknowledge, John Stuart Mill’s classic philosophical justification for freedom of expression – “the clearer perception and livelier impression of truth [is] produced by its collision with error” – looks shaky in the face of the empirical evidence of recent years.

So what should the media’s response be? The idea that journalists should simply report blatant lies neutrally along with contrary information, and let audiences make up their own minds, feels to most journalists like a dereliction of a fundamental responsibility to inform and be fair to the public.

One temptation is to take the lies for granted, to focus on policies. I confess I’ve felt that urge at times, when Trump comes out with yet more mendacious rubbish. Is one more debunking exercise really going to achieve anything?

But that’s surely an abdication of responsibility, too. For lies on this scale and with this malevolent intent corrupt the public realm and erode our democracy, which ultimately relies on some acceptance of shared truth.

We should recognise them for what they are: an authoritarian attack on pluralist institutions. And one that’s disturbingly familiar from the last century of world history. “Contempt for truth goes hand in hand with political oppression,” observes Lee McIntyre of Boston University.

However the media deals with them, we must never deceive ourselves into thinking that the brazen lies of Trump – and the lies of any politician in an open and democratic society – are harmless.