President Trump’s Wednesday night interview with ABC’s David Muir suggested a very simple explanation of why he continues to make outrageous and false claims about voter fraud and crowd sizes: motivated reasoning.

This is the lens through which Trump’s repeated, easily disproven claims make sense. Trump believes that he’s a popular president, swept into office in a popular uprising, with a strong mandate. He starts with that belief and works backward. He fabricates claims to support it. If some of the fabricated evidence falls short — by, say, implying that he was elected in a corrupt election defined by copious voter fraud — he just shifts the fabricated evidence so it serves its intended purpose again.

Psychologists call this phenomenon “motivated reasoning,” and it’s incredibly common. But we’re only now starting to see just how destructive having someone who engages in it constantly in the White House can be.

How Donald Trump deals with contradictory evidence

In the case of the popular vote, Trump’s answer is to double down in his claims that 3 million to 5 million people voted illegally in the presidential election. Trump has cited this obvious falsehood in the past to claim that he won a majority of legitimate votes — and that his presidency thus has a popular mandate, and he did not merely defeat Hillary Clinton due to the geographic whims of the Electoral College. And he does that again with Muir, even more explicitly.

First, he cites a Pew Center on the States report as lending support for these voter fraud claims. Muir points out that David Becker, who wrote the Pew report, has claimed this is a grievous misreading and that there was no significant voter fraud in 2016. Trump got immediately defensive, repeatedly interrupting Muir to ask, “Then why did he write the report?” and attacking Becker for “groveling,” and insisting that it doesn’t matter because there’s plenty of other evidence anyway: “You’re telling me Pew report has all of a sudden changed. But you have other reports and you have other statements.”

But the real giveaway comes when Muir asks if Trump thinks “talking about millions of illegal votes is dangerous to this country without presenting the evidence. … You don't think it undermines your credibility if there’s no evidence?” This is clearly a question about Trump’s ability to perform the duties of president, about his standing with the American people and with the international community.

Trump does not interpret it that way. He interprets it as a challenge to his legitimacy as president, and to his level of popularity. “Those were Hillary votes. And if you look at it, they all voted for Hillary. They all voted for Hillary. They didn't vote for me. I don't believe I got one. Okay, these are people that voted for Hillary Clinton.”

Now, this is clearly nonsense — the idea that an election could have millions of illegal votes, and that all of these votes would go to one candidate and none to that candidate’s rival. Trump is also imagining a shockingly incompetent Democratic conspiracy, in which the Clinton campaign and its allies conspired to dramatically run up the margins in California, New York, and Illinois but just didn’t bother to throw any of these fake votes to Wisconsin, Michigan, or Pennsylvania.

But it makes sense if you view Trump as working backward from faith in his own popularity. It’s a nonsense claim tailor-made to shore up that conviction.

The same goes with his insistence to Muir that he saw record inauguration crowds. This is contradicted by obvious photographic evidence, of course, so Trump repeats talking points about camera angles so his belief that he’s a popular president capable of gathering massive crowds is unchallenged. But he does something more interesting than that too. He challenges the claim that he had a fairly small inaugural crowd not on the grounds that it’s wrong, but on the grounds that it’s insulting.

“Part of my whole victory was that the men and women of this country who have been forgotten will never be forgotten again,” he tells Muir. “Part of that is when they try and demean me unfairly 'cause we had a massive crowd of people. … I won't allow you or other people like you to demean that crowd and to demean the people that came to Washington, DC, from faraway places because they like me.”

Now, Trump is claiming that he’s pushing back on behalf of his supporters, but it’s clear here that he’s mostly upset about the crowd size issue because he finds it demeaning to him. Look at how he refers to his supporters: “people that came to Washington, DC, from faraway places because they like me.” He’s protective of them entirely because they serve as evidence of his own personal popularity. He’s making the subtext — him rejecting these facts because they violate his own belief that he’s popular — text here.

Incidentally, this theory also helps explain Trump’s insistence that approval ratings suggesting he’s the least popular new president in modern history are rigged:

The same people who did the phony election polls, and were so wrong, are now doing approval rating polls. They are rigged just like before. — Donald J. Trump (@realDonaldTrump) January 17, 2017

It’s yet another case of Trump reacting to evidence that contradicts his beliefs by trying to debunk that evidence rather than revising those beliefs at all.

Everyone engages in motivated reasoning to some degree. But this is an extreme case.

Motivated reasoning is not some obscure malady from which only Trump and a handful of other unfortunate folks suffer. It’s a universal aspect of human cognition, and all of us engage in it to some degree or another. And it’s a particularly powerful force in politics, where everyday voters tend to start with an identity — framed most strongly by partisanship but also by race, income, and gender — and then adopt beliefs based on that identity, rejecting attempts at debunking that might threaten those beliefs or identity.

You can see this in how readily voters shift positions in response to partisan cues. Since the start of the 2016 general election, the share of Democrats characterizing Russia as a major threat doubled, as the GOP presidential nominee aligned with the country and Hillary Clinton and allies criticized it. The share of Republicans saying the same fell, and between 2014 and November 2016 Vladimir Putin went from a negative 66 point net approval rating among Republicans to a negative 10 point one, as Trump’s embrace of Putin rippled through the party. These changes can’t be because of changes in Putin’s behavior; his airstrikes slaughtering civilians in Syria and his close relationship with Iran can’t possibly explain Republicans warming to him. Trump can.

Having more information actually makes this effect worse. In a 2006 paper, political scientists Christopher Achen and Larry Bartels found that more-informed Republican voters were more likely to say, falsely, that Bill Clinton had increased the budget deficit than less-informed voters were; they had received more partisan cues. Same goes for well-informed Democrats asked if inflation went down under Ronald Reagan.

And merely debunking falsehoods can actually entrench them deeper. Dartmouth political scientist Brendan Nyhan and the University of Exeter's Jason Reifler have conducted multiple studies that show correcting people's incorrect views about, say, the presence of WMDs in Iraq can actually backfire and make them hold their wrong beliefs even more firmly. This, it would appear, is what happens when one tries to correct Donald Trump.

This is an unfortunate tendency in an electorate but a potentially disastrous one in a president. All presidents have to make thousands of decisions on the basis of fairly limited information that affect millions if not billions of people. Some of those decisions they’re going to get wrong, and if and when that happens, they need to be able to absorb information suggesting their plans aren’t working and adjust accordingly.

When Ronald Reagan’s tax cuts wound up reducing revenue excessively, he signed a law hiking taxes the following year. When HealthCare.gov was malfunctioning, Barack Obama didn’t continue to insist that it was working fine; he brought in coders from Silicon Valley who fixed it and wound up creating two new agencies devoted to improving government IT.

Given the profound degree to which Trump has shown himself to engage in motivated reasoning, do we have any faith he’ll adjust in a similar manner? If he comes out with an Obamacare repeal-and-replace plan that the Congressional Budget Office says will cause 20 million people to lose health insurance, will he change the plan? Or will he reject the CBO evidence, just as he rejects evidence on voter fraud and crowd sizes?

If Trump sends federal troops into Chicago to stop the violence and homicide rates instead spike, will he accept that he screwed up and back down? If Trump withdraws from NAFTA and other trade deals and manufacturing jobs don’t come back, will he try a different approach?

It’s hard to admit you’ve made a mistake and adjust accordingly, but past presidents have often been able to do it. Even George W. Bush, an unusually stubborn president, conceded his Iraq strategy was failing in late 2006 and switched course. But Trump’s early days in office have suggested that he totally lacks this ability. He has no mechanism for absorbing information that conflicts with his preexisting beliefs. And that’s a very dangerous quality in a president indeed.