President Biden’s fall at the U.S. Air Force Academy commencement is proving that while gravity affects all bodies equally, when that body belongs to a commander-in-chief, it can have a varied impact on governing.

The century-old joke, “Watch that first step; it’s a doozy,” is good advice for Mr. Biden who, at 80, sets each day a record for the oldest man to hold the office. Should he complete a second term, he’ll be twice the age upon leaving the White House that President Theodore Roosevelt was upon entering it.

Last month’s Washington Post-ABC News poll put Mr. Biden’s age in election context, with only a third saying he’s in “good enough physical health for the job,” an impression cemented by his falls everywhere from the steps of Air Force One to his bicycle.

There are few places for a modern president to hide from embarrassment or ill health, which is why although only the first dogs witnessed President George W. Bush passing out in the East Wing, he reported it, needing to explain the resulting black eye.

Mr. Biden has quick rhetorical reflexes if not physical ones. He blamed a sandbag for Thursday’s incident and a toe clip for the bike crash. Perception, however, is reality when it comes to surefootedness. President Ford was one of our most athletic leaders, but Chevy Chase portrayed him as a bumbler after a somersault down the Air Force One staircase.  

When reporters asked the Democratic presidential candidate in 2004, Secretary Kerry, about his fall on a snowboard, he said, “I don’t fall,” and pointed to a Secret Service agent. “That son of a bitch ran into me,” a reaction that did nothing to help his image.

In 1996, Senator Robert Dole, the Republican presidential candidate, handled falling off a stage thanks to an unsecure railing with more dignity. Quipping that he’d used “enough hairspray” that at least his hair wasn’t mussed, he then had the shrewdness to joke that he’d “earned his third Purple Heart,” reminding voters of the World War II injuries that incapacitated his right arm, rendering it useless in breaking his fall.

Ford, Dole, and Mr. Kerry may have bruised their presidential chances with pratfalls, but pre-TV candidates who suffered far worse injuries got up and dusted themselves off with no one the wiser, such as President Jefferson, who in 1786 fractured his wrist jumping a fence in Paris.

During the Mexican-American War, the horse being ridden by a future president, Franklin Pierce, reared, smashing his pelvis into the saddle horn and knocking him to the ground where the animal collapsed onto his knee. When Pierce fainted, a soldier under his command called him “a damned coward.”

Pierce refused orders to withdraw but passed out again the next day after reinjuring the knee under enemy fire. Upon regaining consciousness, he asked to be left on the battlefield to die with what remained of his dignity. Yet Pierce survived and went on to be elected president in 1852.

The author of “1920: The Year of the Six Presidents,” David Pietrusza, begins the book, “The president of the United States,” as in President Wilson, “lay bleeding on the bathroom floor,” unable to move or speak thanks to a stroke kept secret even from his vice president.

Mr. Pietrusza also shared an anecdote from his book, “Roosevelt Sweeps Nation.” In it, a crowd shoved President Franklin Roosevelt’s son, James, into his father which “snapped a pin out of one of Franklin’s leg braces and he tumbled downward” on a ramp used for his wheelchair.

A Secret Service agent caught the paralyzed president, “struggling to keep Roosevelt from hitting the ground” and disaster. “FDR did his best,” Mr. Pietrusza writes, “which was always very good, to keep up appearances — waving and smiling — but underneath it all thoroughly infuriated…”

Mr. Biden’s fall won’t be the last to endanger a president or to inspire White House spinmeisters to quote Theodore Roosevelt: “It is not the critic who counts, not the man who points out how the strong man stumbles.”

Regardless, where our presidents walk, the fate of the nation follows, so it’s best that they be honest about their physical health, keep a smile on their faces, and — most of all — watch that first step. It is, even for presidents, a doozy.