The stress of the coronavirus pandemic is testing even the closest relationships.
President Trump and Fox News are no exception.
In a dust-up between the top-rated cable news channel and its most prominent loyal viewer, Mr. Trump unleashed a barrage against the Fox News anchor Neil Cavuto, who gave a withering on-air assessment of the president’s announcement that he was ingesting hydroxychloroquine, a malaria drug that can pose dangers for coronavirus patients.
By Tuesday morning, the president had apparently warmed to the network again, congratulating the morning show “Fox & Friends” on its high ratings. But the fissure underscored Mr. Trump’s keen sensitivity to any hint of criticism from his preferred TV network, where star pundits like Sean Hannity and Steve Doocy have made prime-time and morning shows into pro-Trump cheering platforms.
Hydroxychloroquine was already a fraught subject at Fox News. The prime-time host Laura Ingraham has relentlessly promoted the drug as a potential cure for the coronavirus, even pitching Mr. Trump in person in the Oval Office. But many medical experts, including some at the Food and Drug Administration, have warned against its use to treat the disease, citing a risk of serious heart problems.
On Monday, Mr. Cavuto was hosting his 4 p.m. show when Mr. Trump told reporters at the White House that he had begun taking hydroxychloroquine as a preventive measure against the coronavirus. When the camera cut to Mr. Cavuto, the anchor looked stricken.
“That was stunning,” Mr. Cavuto told viewers, going on to cite studies about the potentially fatal effects of hydroxychloroquine on older patients and those with heart conditions.
“If you are in a risky population here and you are taking this as a preventive treatment to ward off the virus — or in a worst-case scenario, you are dealing with the virus and you are in this vulnerable population — it will kill you,” Mr. Cavuto said. “I cannot stress enough: This will kill you.”
Mr. Cavuto is himself part of a vulnerable population. He has multiple sclerosis, underwent emergency heart surgery in 2016, and survived Hodgkin’s lymphoma in his 20s. Since the coronavirus outbreak, he has regularly warned viewers about the risks of hydroxychloroquine and, more broadly, the medical danger of a premature end to quarantines.
Fox News declined to comment on Mr. Trump’s attacks. (One network personality, the meteorologist Janice Dean, defended Mr. Cavuto on Twitter, writing: “I agree with Neil. You can’t just throw the drug around like it’s a cure. It’s not.”)
On Tuesday, after Mr. Trump again used a White House appearance to promote the drug, Mr. Cavuto re-upped his rebuttal.
“The issue here is whether it’s advisable to take to ward off Covid-19, and no less than the Food and Drug Administration warned back on April 24 that hydroxychloroquine and chloroquine have not been shown to be safe and effective for treating or preventing Covid-19,” Mr. Cavuto told viewers.
Mr. Cavuto was not the only Fox News figure to offer on-air criticism of Mr. Trump’s support of the drug. The network’s senior managing editor for health news, Dr. Manny Alvarez, appeared on Bret Baier’s Monday newscast and called the president’s words “highly irresponsible.”
The view was rosier from the conservative voices on Fox News’s most-watched opinion programs.
Minutes after Mr. Cavuto’s Monday broadcast, the talk show “The Five” offered up hosannas to the president. “When you get this drug to people who can tolerate it, I don’t think you can have any kind of heart condition or arrhythmias and things like that,” said the co-host Greg Gutfeld.
Mr. Gutfeld also dismissed a Veterans Affairs study showing a link between the drug and an increased risk of death in coronavirus patients, asserting that the results had been hyped by journalists who “wanted that drug to be a failure because they want Trump to fail.”
On Tuesday’s “Fox & Friends,” the co-host Brian Kilmeade highlighted studies in France and China that are often cited by the drug’s proponents. “Don’t act like he just grabbed it from some witch doctor,” he said of Mr. Trump.
And Ms. Ingraham, who has resumed her frequent promotion of the drug, booked a doctor on her Monday show who called the drug “life-changing.”
“The people of the United States need to know that they have a brilliant president of the United States, and that he wants to keep himself safe and healthy so that he can guide us through this pandemic,” Dr. Ivette Lozano, a Texas clinician, told Ms. Ingraham.
She added: “Doctors need to start prescribing it immediately.”
Hydroxychloroquine has been prescribed by doctors around the country, who often cite the speed and severity of the coronavirus as a reason to try any medicinal tools available. Rigorous studies have failed to produce data showing significant benefits, and the F.D.A. said last month that hydroxychloroquine should not be used outside clinical trials or situations where a patient can be closely monitored.
Ms. Ingraham offered her viewers some caveats, noting that “studies are still coming in.” But she left an impression that skeptics of hydroxychloroquine were fueled by animus toward the president.
“Look, people should be monitored,” Ms. Ingraham said. “But I think people aren’t getting it when perhaps — I say perhaps, I’m not a doctor — it could actually benefit them. And it’s very safe.”