Editor's note: As presidential candidates Donald Trump and Hillary Clinton prepare to face off in their first debate this week, Allan B. Schwartz, M.D., a professor of medicine in the Division of Nephrology & Hypertension at Drexel University College of Medicine, considers the role that health played in a pivotal contest.

The first-ever U.S. presidential debate to be broadcast live was held in Chicago on Sept. 26, 1960, before more than 77 million television viewers. The candidates had prepared quite differently for the debate. John F. Kennedy had rehearsed his talking points, spending the weekend with aides in a hotel, focusing on the upcoming challenge.

Richard Nixon, on the other hand, spent the day campaigning, and arrived for the debate "in pain, looked green, sallow, and needed a shave," one commentator noted.

Kennedy looked to have a perpetual tan, an apparent sign of health that really may have been a sign of his Addison's disease. He declined to have makeup applied in the TV studio.

Nixon declined, too, afraid it would become known that he had accepted makeup when Kennedy had not. Nixon instead had an aide apply Lazy Shave, a drugstore product, to cover his prominent five o'clock shadow.

The debate agenda included domestic topics such as cutting the national debt, improving schools, and farm subsidies. Both candidates spoke without error, and many in the radio listening audience gave Nixon the edge.

But most Americans watched it on TV. Viewers were overwhelmingly impressed by JFK's confident appearance and organized performance. In contrast, a sweaty Nixon looked anxious before the hot TV lights, and had to frequently dab his face with his handkerchief. The Lazy Shave melted off.

Did Richard Nixon have acute anxiety? His visits to a psychotherapist had been widely rumored, and it later turned out that, indeed, Nixon had been seeing double-board-certified psychiatrist and internist Arnold Hutschnecker since the early 1950s.

Hutschnecker was a psychosomatic-illness specialist whom Nixon consulted for pain in his neck and back plus insomnia after reading the doctor's book, The Will to Live. The psychotherapist treated Nixon for stress and later said that Nixon had "a good portion of neurotic symptoms."

Hutschnecker advised Nixon on how to look calm in his TV debate against the famously cool Kennedy. So why did Nixon not only look anxious but also perspire so heavily that he appeared to have a fever?

Solution:

What voters did not know was that on Aug. 17, 1960, just 40 days before the debate, Nixon scraped his left knee on a car door while campaigning in North Carolina.

He soon developed a Staphylococcus aureus infection. The knee became tender, red, and swollen. Nixon was admitted to Walter Reed Army Medical Center for 12 days of treatment, including surgery on his injured knee and antibiotics.

Nixon was discharged to continue his campaign promise to visit all 50 states, but he was undoubtedly weak, having lost 20 pounds during his ordeal.

Indeed, the night before the debate, Nixon had been feverish. On arrival at the CBS studio in Chicago, he again hit his already tender knee on a car door, undoubtedly adding to his misery and his pallor.

Backstage, he refused to take the advice of CBS producer Don Hewitt to use professional makeup.

Though he sounded polished, Nixon looked pale and sweaty, communicating anxiety that many believe may have lost him not only the TV debate but also the election.

Kennedy beat Nixon in the popular vote by only 112,827 ballots out of more than 68 million cast - not quite 0.2 percent. Kennedy himself said later, after the election, "It was TV more than anything else that turned the tide."

But while even a healthy Nixon likely wouldn't have appeared as suave as Kennedy, he might have held his own in front of the TV audience.

The course of history might have been set not by the debate, but by a knee scrape on a dirty car door.