The arrangement seemed a happy one. But then, the coronavirus happened.

By January, Lachlan Murdoch knew the virus was coming. He’d been getting regular updates from the family’s political allies and journalists in his father’s native Australia, an Australian News Corporation staff member told me. The Fox host he’s closest to, Mr. Carlson, had been a rare voice on the network urging Mr. Trump to act more urgently. Even Mr. Hannity had hosted Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, early on his show and warned of the risks.

But as the crisis took hold, there were more than two weeks of statements like Laura Ingraham’s assertion on Feb. 27 that Democratic criticism was “more unsettling” than the virus and Mr. Hannity’s allegation on March 9 that political opponents were trying to “bludgeon Trump with this new hoax.” Finally, after an obscure Fox Business host, Trish Regan, ranted that the coronavirus issue was “another attempt to impeach the president,” the network pivoted.

The damage Fox did appears likely to extend beyond the typical media hits and misses. I asked Ashish Jha, the director of the Harvard Global Public Health Institute, who appeared on Fox News recently, whether he believes people will die because of Fox’s coverage.

“Yes,” he said. “Some commentators in the right-wing media spread a very specific type of misinformation that I think has been very harmful.”

The communications chief at Fox News, Irena Briganti, said, “The cherry picking of clips from our opinion programs is the definition of politicizing this serious threat, as is irresponsibly attacking Fox News in the middle of a pandemic that has evolved considerably over the last few weeks.” She added, “Suzanne Scott’s exceptional leadership of Fox News Media throughout this crisis is unprecedented, and she is committed to both protecting our employees while keeping the audience informed 24/7 on all our platforms and providing an important public service.”

There are a lot of theories about what went wrong at Fox: that the network’s dug-in hostility toward climate science spilled over to medicine, or that its executives cared about ratings above all else. But interviews with 20 current and former Fox staff members and Murdoch family associates in recent days paint a different picture: The network is in thrall to the president and largely beyond the control of the family that owns it.

When Lachlan Murdoch started to hear complaints about the coronavirus coverage on Fox, a person who has spoken to him said, he mistook it for the usual partisan noise.