The malaria drug chloroquine was developed from quinine, an alkaloid found in the bark of the cinchona tree, which grows in the tropical highlands of South America. The Incas passed the bark cure to Jesuit priests, who transported it to Europe in the mid-sixteen-hundreds. The National Institutes of Health calls quinine “the most serendipitous medical discovery of the 17th century,” but its side effects—diarrhea, vomiting, partial deafness and blindness—could be devastating. A less toxic derivative of chloroquine, hydroxychloroquine, was developed in the nineteen-forties. Doctors and pharmacists call it HCQ.

Against malaria, the drugs, which are taken as pills, essentially defend red blood cells against a parasite that is transmitted by mosquito bite. Lately, some doctors have been trying it against the novel coronavirus, which causes COVID-19. Attention to chloroquine and hydroxychloroquine—and to a third drug, the antibiotic azithromycin, a common brand name of which is Zithromax Z-Pak—intensified in mid-March, after researchers at Aix-Marseille University, in France, released a preliminary study saying that, in a clinical trial, the combination of hydroxychloroquine and azithromycin had quickly reduced the amount of the virus in COVID-19 patients.

On March 18th, on Fox News, Tucker Carlson opened a three-minute segment about the study by saying, of the United States, “This is a country of science.” He then introduced a lawyer, Gregory Rigano, whom he identified as an adviser to Stanford University’s medical school. Rigano had self-published a white paper about chloroquine, on Google Docs; his connection to the French research was otherwise unclear. He was appearing remotely, wearing a suit and sitting in front of a cold fireplace. When Carlson asked him why he thought the study was important, Rigano responded, “The President has the authority to authorize the use of hydroxychloroquine against coronavirus immediately. He has cut more red tape at the F.D.A. than any other President in history.”

According to his Web site, covidtrial.io, Rigano has experience “advancing various pharmaceutical assets through laboratory, animal, formulation, manufacturing, clinical trials,” and was hosting an “open data clinical trial for Covid-19.” (The wording on the Web site has since been changed.) He told Carlson that the French study “was released this morning on my Twitter account,” and showed a “one hundred per cent cure rate” against the coronavirus. Carlson called the revelation “remarkable.” Rigano, after a bizarre reference to hepatitis, said, “What we’re here to announce is the second cure to a virus of all time.”

Charlie Kirk, the founder of the conservative nonprofit Turning Point USA, tweeted the segment, exhorting his nearly two million followers to “RT If President @realDonaldTrump should immediately move to make this available.” Most media outlets, though, quickly challenged the credibility of Rigano and that of his white paper’s co-author, James Todaro, a cryptocurrency investor who has tweeted about having a medical degree from Columbia. HuffPost called them “hucksters.” Joan Donovan, who studies “media manipulation and disinformation campaigns” at the Shorenstein Center, at the Harvard Kennedy School, called them “bitcoin entrepreneurs” and pointed out that “neither do research on viruses.” She wrote, “This is dangerous because people are now tweeting about trying to get their doctors to prescribe anti-malaria drugs. Worse, thousands of people think they can cure coronavirus by drinking tonic water.” (Tonic water contains quinine.) Stanford Health Care posted an “IMPORTANT NOTICE” on its Web site: “A widely circulating Google document claiming to have identified a potential treatment for COVID-19 in consultation with Stanford’s School of Medicine is not legitimate.”

Donald Trump, however, ran with it. Last Thursday, at a press conference, he declared that chloroquine had “been approved” by the Food and Drug Administration as a treatment for COVID-19. (It hadn’t.) On Friday, he said that he is “a big fan” of the drug. (The F.D.A. commissioner, Stephen Hahn, issued a cautionary statement about spreading “false hope.”) On Saturday, Trump tweeted, “HYDROXYCHLOROQUINE & AZITHROMYCIN, taken together, have a real chance to be one of the biggest game changers in the history of medicine.” He added that the drugs should be used “IMMEDIATELY” to treat the coronavirus. HCQ is also used to treat rheumatoid arthritis and lupus, which are autoimmune diseases; at one of his pressers, Trump had said, “If you wanted, you can have a prescription,” adding, “What the hell do you have to lose?”

Physicians responded instantly and publicly. Sam Ghali, an emergency physician in Lexington, Kentucky, tweeted that the President’s recommendation involved “a DANGEROUS combination of drugs with tons of side effects,” and that “together they can make your heart go into abnormal rhythms and even KILL you.” Rob Davidson, an emergency physician in western Michigan, who chairs the Committee to Protect Medicare, tweeted, at Trump, “Leave the medical advice to doctors. You can’t even do your own job correctly, stop trying to do ours.”

The American Society of Health-System Pharmacists soon reported a shortage of HCQ. By Sunday, at least four state pharmacy boards—in Idaho, Ohio, Nevada, and Texas—had restricted prescriptions. (The list has now grown to include Kentucky, North Carolina, and Oklahoma.) At least one board also restricted azithromycin. Katherine Rowland, a pharmacist in Eugene, Oregon, tweeted, “Well it finally happened to me. A dentist just tried to call in scripts for hydroxychloroquine + azithromycin for himself, his wife, & another couple (friends). NOPE. I have patients with lupus that have been on HCQ for YEARS and now can’t get it because it’s on backorder.” A lupus patient in Maryland told a reporter for Undark Magazine that she never worried about a drug shortage but was now terrified that, without the medication that protects her organs from inflammation, her immune system would turn on her. “I’ll suffocate,” she said.

In recent weeks—as the number of coronavirus cases escalated to what is now half a million worldwide—the F.D.A. and the Federal Trade Commission have sent cease-and-desist letters to at least seven sellers of products that are being marketed as cures for the coronavirus. On March 6th, one such warning went to “The Jim Bakker Show,” in Blue Eye, Missouri. The television program, which is fronted by a televangelist who spent nearly five years in prison, in the early nineteen-nineties, for fraud, had been touting survivalist products, including Silver Sol Liquid, a silver solution that was purported to “mitigate, prevent, treat, diagnose, or cure COVID-19 in people.” Viewers were told that they could put the liquid “in a nebulizer which then creates a steam and you breathe it in, and it will go directly into your lungs where that virus is.” Another letter went to Herbal Amy, an L.L.C. in Nampa, Idaho, the Web site of which was selling “Coronavirus Protocol” products: Coronavirus Boneset Tea, Coronavirus Cell Protection. The suggested regimen was “rather extensive,” because “the particular corona virus that is now spreading world wide is exceptionally potent,” the Web site noted. The herbs in the protocol were “specific in one way or another” for the virus, and worked “for acute infections.”

Anthony Fauci has directed the National Institute of Allergy and Infectious Diseases since Ronald Reagan was President. As a medical professional, he has faced H.I.V., SARS, MERS, Ebola, and now Trump. At press conferences, Trump speaks of hunches (“I feel good about it”); Fauci delivers information that has been vetted by experts. On Sunday, Science magazine asked Fauci how he can tolerate statements that “aren’t true and aren’t factual”; Fauci replied, “I can’t jump in front of the microphone and push him down.” Fauci carefully explained that any clinical successes related to the cocktail that Trump was praising were anecdotal. He said, “My job is to ultimately prove without a doubt that a drug is not only safe but that it works.”

As the coronavirus continued to spread, Trump made one troubling declaration after another. A vaccine was coming “relatively soon,” he said. (It takes at least a year to develop a vaccine.) “We were very prepared” for a pandemic, he said. (The country’s hospitals were caught with such a shortage of basic protective gear that front-line health-care workers are reusing, by necessity, potentially contaminated masks). The virus “miraculously goes away” as the weather warms, he said. (Robert Redfield, the director of the Centers for Disease Control and Prevention, has said, “This virus is probably with us beyond this season, beyond this year.”) The number of coronavirus patients would be “close to zero,” Trump said. (At least a thousand people have died of the coronavirus in the United States, thirteen of them in one twenty-four-hour period, this week, at a single hospital in Elmhurst, Queens.) By Wednesday night, on Twitter, #DoctorsOnlyPressConferences was trending nationally.