The reckoning that Robert Califf spent years warning about began, as so many things seem to these days, on social media. It was October 2024. His tenure as commissioner of the Food and Drug Administration was winding down, and he was starting to imagine a happy retirement surrounded by grandchildren when he noticed Robert F. Kennedy Jr. taking aim at his agency, and the 19,000 or so people who worked there, on X.

“FDA’s war on public health is about to end,” Kennedy wrote. “This includes its aggressive suppression of psychedelics, peptides, stem cells, raw milk, hyperbaric therapies, chelating compounds, ivermectin, hydroxychloroquine, vitamins, clean foods, sunshine, exercise, nutraceuticals and anything else that advances human health and can’t be patented by Pharma. If you work for the FDA and are part of this corrupt system, I have two messages for you. 1. Preserve your records, and 2. Pack your bags.”

It was a confused, almost comically pompous declaration, Califf recalls thinking, and it ought to have been the least of his concerns. Kennedy had not yet been tapped to serve as anything, let alone the highest health official in the land. Still, it struck a nerve. More and more, people seemed to clamor for things that were unproven, to question things that were and to express not only mistrust but outright hostility toward the doctors, scientists and civil servants trying to separate one from the other. That hostility was being nourished by exactly the kind of mis- and disinformation Kennedy was espousing. It was easy to paint the F.D.A. as a supervillain (an aggressive suppressor of sunlight, vitamins and exercise, to borrow Kennedy’s language), in part because the truth was so much more complex.