Anthony S. Fauci was swamped by so many angry messages and threats that in late October his assistant quit answering the phone for two weeks. The U.S. covid chief got 3,600 phone calls in 36 hours, just as he and other Biden administration officials were preparing for the campaign to vaccinate young children.

Much of the onslaught stemmed from a viral and false claim that the agency Fauci leads, the National Institute of Allergy and Infectious Diseases, had funded a medical experiment in which beagles were trapped in mesh cages filled with diseased sand flies, according to four National Institutes of Health officials familiar with the calls. The outrage was supercharged by a bipartisan letter signed by 24 members of Congress that questioned the agency’s funding of medical research on dogs.

“You worthless piece of s—, you should be put in prison. Torturing animals!” said a caller in one of 15 voice mails obtained by The Washington Post. “I’d like to take you out in the sand, tie you down, put them fleas all over your a–.”