“To say he’s out of the mainstream would be an understatement,” said Dr. Ashish K. Jha, dean of the Brown University School of Public Health. “His views are not only very unorthodox – they do not make any sense.”

The Florida Department of Health did not respond to The New York Times’ requests to interview Dr. Ladapo.

Before the pandemic, Dr. Ladapo, 43, who immigrated from Nigeria when he was 5, was an accomplished clinical researcher at UCLA, with degrees from Harvard in medicine and health policy. He focused on topics like smoking cessation and cardiovascular risk for HIV patients.

In early 2020, he contacted Dr. Jeffrey Klausner, a professor of medicine at the University of Southern California, to discuss lockdowns, which Dr. Klausner saw as having limited utility.

Dr. Ladapo did not want to take policies at face value, Dr. Klausner said: “He was the kind of guy who’s going to be reading an article in the medical or scientific literature and then going to the references, digging up those references, and then going to the references of those references. ”

In April 2020, Dr. Ladapo published an opinion essay in The Wall Street Journal, titled “Lockdowns Won’t Stop the Spread.” He argued that it was too late to stop the altogether virus, so policymakers should consider the heavy toll of shutdowns and not just “the singular goal of reducing Covid-19 deaths.”

His national profile grew. More opinion pieces followed.

A few months later, Dr. Ladapo appeared clad in a white medical coat on the steps of the United States Capitol with a group of people who called themselves “America’s Frontline Doctors.” Some physicians in the group gave misleading claims about the virus, including that the drug hydroxychloroquine was an effective treatment. The Food and Drug Administration advises otherwise, warning that it could cause irregular heart rhythms.