One year into U.S. President Donald Trump’s second term, questions about his health and competence are as pervasive as the gilt sprawling through the Oval Office.

These questions grew even louder following his rambling speech this week at Davos, where he repeatedly referred to Greenland as Iceland, falsely claimed the United States gave the island back to Denmark during the Second World War and boasted that only recently, NATO leaders had been lauding his leadership (“They called me ‘daddy,’ right?”).

Read more: Trump's annexation of Greenland seemed imminent. Now it's on much shakier ground

Do swollen ankles and whopping hand bruises signal other serious problems? Do other Davos-like distortions and ramblings — plus a tendency to fall asleep during meetings — reveal mental decline even more startling than Joe Biden’s in the final couple of years of his presidency?

This is not the first time in White House history that American citizens have had concerns about the health of their president — nor the first time that historians like me have raised questions.

The experiences of Trump’s predecessors remind us of the dangers inherent in the inevitable human frailty of the very powerful.

Frailty can entail crises in physical health like William Henry Harrison’s 1841 death from pneumonia 32 days after his inauguration or Warren G. Harding’s heart attack and death in 1923.

Frailty can also involve weaknesses in brain function, which impact the capacity for analysis and problem-solving.

Bodily trauma can have obvious effects on presidential competence. Sometimes it’s a temporary impact, as with Dwight D. Eisenhower’s 1955 heart attack and recovery. But sometimes it’s permanent: Woodrow Wilson never recovered his capacities after an October 1919 stroke, with White House leadership languishing for 18 months under his wife’s gatekeeping until his death.

In other cases, the effect of physical ailments on competence was less clear — and therefore debatable. Franklin D. Roosevelt’s heart........

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