“We will make Americans healthy again,” Robert F. Kennedy Jr. has declared. A political action committee that has promoted Mr. Kennedy, President-elect Donald J. Trump’s pick for health and human services secretary, says his movement is “igniting a health revolution in America.”

But the word “again” presumes a time in the country’s past when Americans were in better health. Was there ever really a time when America was healthier?

For historians of medicine, there is a short answer.

“No,” said Nancy Tomes, a historian at Stony Brook University.

John Harley Warner, a historian at Yale, said, “It’s hard for me to think of a time when America, with all the real health disparities that characterize our system, was healthier.”

Dr. Jeremy Greene, a historian at Johns Hopkins University, asked: “Which particular era does R.F.K. want to take us back to?”

Probably not the 19th and early 20th century.

Rich men smoked cigarettes and cigars, the poor chewed tobacco. Heavy drinking was the norm.