President Trump’s open-mic riff suggesting government health experts explore injecting patients with bleach or household disinfectants to fight covid-19 made for easy parody. “And then I see the disinfectant, that knocks it out in a minute, one minute,” he said at Thursday night’s televised news briefing. “Is there a way we can do something like that, by injection, inside, or almost a cleaning.” Because the coronavirus “does a tremendous number on the lungs,” he went on to say, “it would be interesting to check that.” He added his usual disclaimer, “I’m not a doctor,” but assured viewers that “I’m, like, a person that has a good you-know-what.”

This prompted warnings from state governments and the makers of Lysol about the serious bodily harm that taking this “I’m-not-a-doctor” advice would cause. But as absurd as the president’s comments were, they could hardly have been surprising. His “good you-know-what” has led us down this path before. During his three years as president, Trump has regularly expressed confidence that he knows more than the experts. That confidence is matched only by the ignorance he actually displays about a vast array of topics. Repeatedly, he has sent government officials scrambling on foolish missions, leading them to spend time and personal capital persuading him not to follow through on schemes that are invariably wasteful, ineffective, unrealistic or dangerous.

Consider, for example, some presidential guidance in 2017: Trump — who has no nautical, military or engineering experience — decided the electromagnetic catapults the Navy planned to install on aircraft carriers to launch airplanes into the sky were technically inferior to the steam catapults used in older-generation ships. “Digital. They have digital. What is digital? And it’s very complicated, you have to be Albert Einstein to figure it out,” the president said in announcing he would order the Navy to replace the new catapults. Though experts say the move would cost billions of dollars and degrade the carriers’ capabilities, Trump has repeatedly returned to the topic in the years since, forcing Navy officials to put on their best game face in public pronouncements about the president’s off-the-wall comments.

A favorite object of Trump’s expertise remains the wall he is attempting to build along the southern border. His outlandish suggestions include proposals to paint it black so it would be too hot to climb, electrify it and cap it with spikes. The New York Times reported that he considered adding a water-filled moat that would be stocked with snakes and alligators, a farcical idea for which aides nonetheless felt compelled to seek a cost estimate. Officials at the Department of Homeland Security and the Army Corps of Engineers have spent months constructing prototypes and convincing the commander in chief to abandon impractical, expensive and constantly changing demands.

The president has a few ideas about the weather, too. During meetings to discuss hurricane response, the president has asked why the government doesn’t just drop a nuclear bomb on hurricanes before they make landfall. Despite the fact that nuking a hurricane would be banned by treaty, would spread radioactive fallout along the hurricane’s path and would do nothing to actually stop the storm, an administration official reportedly told the president, “Sir, we’ll look into that.”

Trump’s “knowledge” of chemistry and physics are joined by an interest in geography. Last August, he repeatedly pushed advisers to consider whether the United States could purchase Greenland from the government of Denmark. When news of his plan leaked and the Danish prime minister publicly responded that Greenland was not for sale, Trump publicly pouted by abruptly canceling a planned meeting with her.

It is tempting to laugh off the president’s most ridiculous ideas as comic relief that will never be implemented because cooler and wiser heads in the government will ultimately prevail. Indeed, the president’s defenders often try to defend his wackiest suggestions by declaring him an innovative thinker, usually just before he hangs them out to dry by denying he said the thing he clearly said or by pretending he was joking, as he did with his comments on disinfectants. “I was asking a question sarcastically,” he said Friday.

But these journeys deep into the abyss of the presidential mind have real effects on the workings of government and the behavior of individual Americans. Officials spend time and resources that should be directed toward addressing actual problems instead of studying Trump’s worst ideas and convincing him to back down. For example, Anthony S. Fauci, the government’s top infectious disease expert, has been forced to intervene repeatedly with the president over policies that Fauci says would compromise public health.

Other officials burn their own hard-earned credibility by publicly defending Trump’s delusions. When Trump initially made his disinfectant recommendation, he paired it with this suggestion: “Supposing we hit the body with a tremendous — whether it’s ultraviolet or just very powerful light — and I think you said that hasn’t been checked but you’re going to test it. And then I said, supposing you brought the light inside the body, which you can do either through the skin or in some other way, and I think you said you’re going to test that too. It sounds interesting.”

The look of obvious discomfort on the face of Deborah Birx, the administration’s coronavirus response coordinator, made her an Internet sensation. A day later, she defended Trump on Fox News by arguing, “when he gets new information he likes to talk that through out loud,” a head-scratching explanation that also contradicted Trump’s remark that he was being sarcastic.

Some of Trump’s silliest ideas actually make it into policy. Just as customs agents can’t catch every vehicle smuggling drugs through the border, government officials can’t prevent every presidential musing from being turned into reality. We now have a Space Force, a new branch of the armed services that cost billions to establish and serves no discernible purpose that wasn’t already being handled elsewhere. Trump’s obsession with the trappings of military pomp eventually got him the Fourth of July gathering he’d long sought, even if the tanks he wanted to parade down the Mall ended up merely parked there instead. He seems intent on recalling a thousand cadets to the U.S. Military Academy so he can deliver a graduation speech, despite the public health risks it will cause.

Beyond Washington, some Trump loyalists have trouble discerning which of his ideas stray from mere quirkiness into the realm of personal danger. When the president repeatedly pushed chloroquine and hydroxychloroquine as a potential “game changer” in the treatment of patients with covid-19, despite an absence of scientific evidence, Americans responded by hoarding and consuming the drugs, sometimes at their own peril. Maryland’s emergency hotline received over 100 calls about disinfectants after Trump’s latest comments. New York City’s poison control center reported a spike in cases of exposure to disinfectants, including Lysol.

But most concerning is the obvious issues these flights of fancy raise about Trump himself and his fitness for public office of any kind, let alone the presidency. Those questions have been apparent throughout his term, as when he claimed that windmills cause cancer (they don’t) or that the F-35 stealth fighter is literally invisible (it’s not). The president of the United States has trouble distinguishing fantasy from reality. He believes he knows more than anyone in the room when in fact he knows less. He can’t admit a mistake, even when doing so would be the smartest way out of the holes he invariably digs for himself.

Those traits were harmful enough when the country was riding high on relative peace and prosperity. During a global pandemic and a disastrous economic downturn, they can prove catastrophic. As Trump’s presumed election opponent, former vice president Joe Biden, tweeted, “I can’t believe I have to say this, but don’t drink bleach.” The warning was specific to Trump’s foray into disinfectants, but it serves as an apt metaphor for his entire presidency.