Saad Omer, director of the Yale Institute for Global Health, said downplaying the risks of a health crisis might relieve panic in the short term. But politicians who mislead the public risk eroding trust in the long term.

“You don’t want to convey the false sense of certainty when the situation is evolving,” Omer said.

Lawrence Gostin, a professor of global health law at Georgetown University and director of the O’Neill Institute for National and Global Health Law, said, “I would say [about] a politician or celebrity that weighs in on a scientific issue against all the evidence, those comments are usually harmful to the population.”

Trump’s recent comments on the soldiers’ wounds and the virus are far from the first time the commander in chief has shared his contrarian notions on health issues. In the past, he’s weighed in on topics ranging from exercising (he’s said it could kill) to football concussions (he said they’re just “a little ding on the head”) to wind turbines (he said “the noise causes cancer”). The new coronavirus, a highly contagious pathogen that originated in China and causes respiratory illness, has infected five people in the U.S. Were it to become a pandemic, it would present Trump with the first major public health emergency of his tenure.

Before he was president, Trump was skeptical of vaccine safety. He repeatedly referenced a debunked theory linking childhood vaccines to an increased risk of autism, though he stopped short of advising parents to stop vaccinating their kids. “To all haters and losers: I am NOT anti-vaccine,” Trump tweeted in 2014, “but I am against shooting massive doses into tiny children. Spread shots out over time.” The CDC’s vaccination plan recommends children get dozens of vaccines before they’re 6, which Trump has called more appropriate for a “horse” than a child.

“People disregard medical advice because it makes them feel empowered,” said Tom Nichols, author of The Death of Expertise, which examines the rise of anti-expertise sentiment. “Trump, who never likes to be the guy who doesn’t know everything, has a vested interest in always rejecting expert advice because he doesn’t like to think that he knows less than anybody else in the room.”

Amid a measles outbreak in 2019, Trump seems to have changed his attitude on vaccines, aligning himself with the medical mainstream and encouraging parents to vaccinate their children. “They have to get the shots,” Trump told reporters, according to ABC News.

But he was inclined to be more alarmist before he took office.

During the height of the Ebola outbreak in 2014, Trump had a lot of advice for then-President Barack Obama, including that he cancel all flights from virus-afflicted areas. (“What the hell is wrong with you?” he sniped at Obama for not instituting a travel ban). He also suggested that Ebola might have some welcome cultural fallout: discouraging people from shaking hands.

But now that he has ascended to the ultimate bully pulpit, the reaction to his half-baked medical opinions has generated outrage as well as raised eyebrows.

In recent days, veterans groups scolded Trump for downplaying the severity of soldiers’ traumatic brain injuries, which some have described as the defining injury of the wars in Iraq and Afghanistan because of the high casualty numbers. Since 2000, more than 413,000 service members have been diagnosed with a traumatic brain injury, which can cause seizures, memory loss, dizziness and slurred speech. Representative Bill Pascrell (D-N.J.), who is co-chairman and founder of the Congressional Brain Injury Task Force, wrote in a letter to the Department of Defense that Trump’s comments show a “clear lack of understanding of the devastating impacts of brain injury.”

Brain injuries have been a hot topic for Trump in recent years. On the campaign trail, Trump teased the NFL for implementing new rules intended to prevent concussions and other brain injuries. “We don’t go by these new, and very much softer, NFL rules,” Trump told a crowd at a campaign rally in Florida. As president, Trump has lamented the rule changes, telling supporters “they’re ruining the game.” Pro football players lambasted the then-candidate after his 2016 rally.

Concussions dropped almost 30 percent during the NFL’s regular season after the rule changes. For his part, Trump seems to have walked back his previous comments, telling CBS’ Margaret Brennan last year he believed football was a “dangerous sport” and that he wouldn’t want his son Barron to play.

Fitness experts would probably wince at Trump’s personal health advice. The president has a well-known love for golf, but he’s no advocate for other forms of exercise. He’s compared the human body to a battery, reportedly saying exercise drains the body’s limited energy reserves. “You’re going to die young because of this,” he told a top casino executive training for an Ironman triathlon. Trump gets his work out by standing in front of an audience for an hour, he explained to the The New York Times in 2015, noting that his friends who exercise often are “a disaster” and require frequent surgeries. Health experts, unsurprisingly, pushed back against Trump’s “battery” analogy.

The president is a self-diagnosed germophobe who hesitates to shake hands and makes ample use of the hand sanitizer his personal aide carries at all times. Last summer, he excoriated acting chief of staff Mick Mulvaney for coughing during an interview with ABC’s George Stephanopoulos. “I don’t like that, you know,” Trump told Mulvaney on camera. “If you’re going to cough, please leave the room.”

Trump has a penchant for Big Macs, too, and in defending his love of junk food he may be one of the few people to advocate for eating processed and fast food. “I like the cleanliness,” the president has said of chains like McDonald’s and Wendy’s. “I think you’re better off going there than someplace you have no idea where the food is coming from.” To his credit, at least one study found that fast food joints are cleaner than fancy restaurants and homes, but it’s been widely accepted that a diet of fries and hamburgers increases the risk of obesity and cancer.

Wind turbines are the real cancer risk, if you take Trump’s word for it. The president has repeatedly warned that the electricity-producing turbines could kill birds, harm children and ruin coastal sightlines off his Scottish golf course. He also claimed, without evidence, that the turbines emit “tremendous fumes” and noises that cause cancer.

Disease researchers disputed Trump’s claim. “The American Cancer Society is unaware of any credible evidence linking the noise from windmills to cancer,” the organization told The New York Times.

Stoking unfounded anxiety, rather than minimizing real risks, is the most dangerous side effect of a high-ranking official or celebrity wading into topics they know little about, public health experts say.

Linda Aldoory, a professor at the University of Maryland who has studied and worked in public health communications, said celebrities and political leaders can shift attitudes and perceptions on public health.

“They can sway our sense of fear,” she said.