Late in Thursday’s debate, President Biden, 81, and former President Donald J. Trump, 78, were asked the looming question: How could they assuage voters’ concerns about their ability to handle the presidency as they continue to age?
Neither man’s answer may have been enough to push aside those qualms.
Mr. Biden, who has faced the more nagging questions about his mental and physical acuity, addressed the concern briefly before shifting topics.
“I spent half my career being criticized being the youngest person in politics,” he said, a common reframe making reference to his youth — 30 years old — when he first became a senator. “And now I’m the oldest. This guy is three years younger, and a lot less competent.”
Mr. Biden then spent the rest of his answer promoting his administration’s accomplishments, meandering through an anecdote about visiting South Korea to encourage semiconductor production in the United States.
Mr. Trump said he had aced cognitive tests and questioned Mr. Biden’s ability to do the same. “We knock on wood wherever we may have wood that I’m in very good health,” he said.
Then he bragged about his golf scores, prompting one of the oddest exchanges of the night.
“He challenged me to a golf match,” Mr. Trump said of his opponent. “He can’t hit a ball 50 yards.”
Mr. Biden replied, “I’d be happy to have a driving contest with him,” saying that his golf handicap when he was vice president was a six, meaning he typically shoots six strokes over par. “I’m happy to play golf with you, if you carry your own bag. Think you can do it?”
“That’s the biggest lie, that he’s a six handicap, of all,” Mr. Trump said, prompting Mr. Biden to begin to explain that he was an eight handicap.
“Let’s not act like children,” Mr. Trump added.