Out tumbled the groundless suspicions of Donald Trump. The hacked Democratic National Committee server was somehow in Ukraine. Barack Obama himself might have ordered spies to infiltrate Trump’s campaign. Thousands of Never Trumpers have been plotting against him since he took office.

For an hour last week, the folks at Fox & Friends struggled to get a word in and elicit some facts, any facts, that might have verified the conspiracy theories the 45th president was breathlessly disgorging. “Who are your sources?” one host asked Trump. “I can’t tell you that,” Trump replied. Are you sure the server is in Ukraine? another asked. “Well, that’s what the word is,” Trump said.

A product of tabloid culture, Trump has long trafficked in conspiracy theories. But as chief executive, he’s used the machinery of government to give the ones especially useful to him the stamp of official validation. (That’s the main reason he now faces impeachment in the House.) These baseless theories are a way for Trump to explain away his problems and undercut opponents. Beyond that, though, they seem to serve distinct emotional needs, feeding a narcissistic ego that cold reality won’t satisfy. His efforts to persuade the public to go along with these self-protective myths have already corroded democratic institutions. The wreckage from that destructive legacy won’t be easily repaired after he leaves the stage.

“We’ve never had a president who trades in conspiracy theories, who prefers lies instead of fact,” Douglas Brinkley, a history professor at Rice University and a presidential historian, told me.

Read: Trump is surrounded

A U.S. president has at his disposal the most authoritative information available on Earth. Yet Trump doesn’t seem to want it. Disdainful of credentialed professionals, Trump has taken extraordinary steps, and spent taxpayer dollars, standing up dubious ideas of his own creation.

In September, with Hurricane Dorian bearing down, Trump clung stubbornly to his claim that the storm’s path put Alabama in jeopardy. The reason isn’t entirely clear, but he may have wanted to come across as the savior of a loyal red state that turns out in force for his rallies. After a local office of the National Weather Service corrected him, the White House intervened, culminating in an official administration statement rebuking a scientific agency that had dared challenge the president’s bogus forecast.

Claiming that millions of people voted illegally in the 2016 election and cost him the popular vote, Trump set up a White House commission to see if there was widespread voter fraud—a nonexistent problem requiring no solution. It disbanded last year without turning up any evidence that Trump was robbed of a popular-vote victory. He also accused Obama's FBI of trying to surveil his campaign from the inside, but the Justice Department inspector general is expected to debunk that claim in an upcoming report.

The Ukraine debacle is the most extreme case, illustrating just what can happen when the president takes hold of a bad idea and won’t let it go. Repellent to Trump is the notion that he would have lost to Hillary Clinton had it not been for Russia’s electoral interference. The self-image he’s constructed rests on the idea that he’s rich and successful—not a “loser,” the epithet he routinely hurls at opponents. Trump has worried that if people believe Russia’s interference spelled the difference in the election, it could undermine his legitimacy, Special Counsel Robert Mueller’s report showed.

All of which explains why, for the president, the Ukraine fiction is so alluring. It’s a twofer. If Ukraine covertly interfered in the election for Clinton’s benefit, as Trump has suggested, that would both exonerate Russia and cement his 2016 victory. Trump apparently finds that theory so compelling that he risked his presidency to see if he could give it traction. Loyal appointees are now pushing his message: In a news conference on Tuesday, Secretary of State Mike Pompeo said that Ukraine merited investigation. The United States has “not only a right, but a duty” to look into any “information that any country has messed with American elections,” Pompeo said.

Trouble is, none of this has a basis in reality. Members of Trump’s own staff and intelligence-community officials have all debunked the idea that the culprit was Ukraine, not Russia.

To grasp why conspiracy theories appeal to Trump, it’s important to understand the man. Mental-health experts have described Trump as a narcissist forever feeding his grandiose sense of self. Facts and evidence aren’t nearly so convincing to Trump as what makes him feel better about himself. Trump was an illegitimate candidate in 2016 who benefited from foreign interference? No, that was Hillary! “His perception, even his definition, of good and bad is what makes him feel good in the moment,” David Reiss, a San Diego–based psychiatrist who has studied and written about Trump’s psyche, told me. “There’s no sense of consequences beyond what’s good for me in the moment, and then that gets projected onto everything. What’s good for me is good for the universe.”

Joseph Vitriol, a College Fellow in Harvard’s psychology department who has studied conspiracy theories, told me that Trump “likely will gravitate toward anything that will make him feel good about himself and believe that he’s respected. That makes him averse to information that’s inconsistent with that perception, and makes him deeply suspicious of the motivations of people who criticize him. It also makes him unable to meaningfully engage with a broad range of information.”

This propensity for self-soothing combines with an anti-intellectualism that seems part of Trump’s makeup. He’s skeptical of elite opinion and not convinced that he has anything still to learn. As my colleague Ron Brownstein wrote last week, Trump and his Republican allies have been “escalating their war on expertise.”

Trump’s mind is thus fertile soil for bogus ideas to take root. A new book written by an anonymous senior Trump-administration official, A Warning, describes Trump pushing away facts and conclusions that don’t jibe with his own views. “When he does sit down for a briefing on sensitive information, it’s the same as any other Trump briefing,” the author writes. “He hears what he wants to hear, and disregards what he doesn’t. Intelligence information must comport to his worldview for it to stick. If it doesn’t, it’s ‘not very good.’”

“He gets his intellectual mojo out of television,” not other forms of learning, said Brinkley, who traveled to Mar-a-Lago during the transition in 2016 to meet with Trump and discuss past presidential inaugurals.

Read: The real story behind the Steele dossier

Conspiracy theory is a convenient umbrella term for various ideas Trump holds that lack foundation. But the phrase may be assigning these notions more gravity than they deserve. Trump often dishes up brute assertions that leave no space for rational argument. Statements that stoke anger, not thought. Democrats are out to get him because they’re “sick.” The impeachment inquiry is a “hoax.” Repeat as needed. Nancy Rosenblum, a government professor emerita at Harvard, describes it as conspiracy without the theory. The term she’s coined for this sort of mind-set: conspiracism.

“There’s no answer for it,” she told me, “which is why it is so seriously disorienting to people. We’ve never seen anything like it. We don’t know how to meet it. It’s an attempt to construct a reality, and when it comes from the president, he has the capacity to impose that reality on the nation.”

Insulating the president from fringe ideas has gotten tougher over time. At a staff meeting early in the term, former White House Chief of Staff Reince Priebus held up a copy of a news article from a dubious source that Trump had seen, a person familiar with the matter told me. Priebus cautioned aides that information that hadn’t been properly vetted shouldn’t cross the president’s desk.

When he succeeded Priebus, John Kelly tried to professionalize Trump’s briefings and see to it that he heard both sides of an argument—the sort of practice that was routine in previous White Houses. To the staff’s frustration, though, Trump would often return to the Oval Office mentioning something he’d seen on cable news the night before and wanting to go in a different direction, forcing aides to scramble, another person familiar with the matter said. Late in Kelly’s tenure, which ended last year, Trump was listening less and less to the advice coming from White House staff and more to that from his own outside sources, this person said. With the arrival of Mick Mulvaney as acting chief of staff at the end of last year, whatever structure was left largely collapsed, people close to the White House told me. Trump gets information how and when he wants.

One source is his phone—a fount of misinformation for anyone with a Twitter addiction. A recent New York Times investigation of Trump’s Twitter habits showed that he has “retweeted at least 145 unverified accounts that have pushed conspiracy or fringe content.” In July, he retweeted a post from one unverified account that said Obama supporters were using protests to undermine his presidency, the paper reported.

Constructing his own reality necessitates an attack on fact-finding institutions that are central to American democracy—universities, nonpartisan government agencies, law enforcement, the intelligence community, and the news media. For Trump’s version of events to take hold, he needs people to accept that the facts leaping out at them aren’t to be believed, that institutions wedded to objective truth aren’t to be trusted.

Here, Trump’s imprint will be hard to erase. Trump acolytes inside the Republican caucus are aping his methods and standing with him as he advances his fact-free claims about Ukraine’s complicity in the 2016 election. Unceasing attacks on “fake news” have resonated with a certain audience. Polling from The Wall Street Journal/NBC News shows that in 2010, 60 percent of Republicans had either no or very little confidence in the national news media. As of June—two and a half years into Trump’s presidency—that figure had grown to 74 percent. “Conspiracy theories go right to the jugular of what a democracy is,” Vitriol said. “The stakes are as high as they could possibly be.”

One day, the conspiracist in chief will leave office. His successors will face a choice: Exploit the damage he’s done to democratic institutions and norms, or see if it can be fixed.