“It has been the greatest honor of my life to serve as your President,” Biden said in a letter he posted to X on Sunday afternoon. His struggles validated concerns of majorities of voters that he would be too old for a second term that would have ended when he is 86. But in the end, Biden could not find a way to make voters unsee the poignant picture of an 81-year-old commander in chief who appeared to have seriously declined and was stumbling in the debate. When Johnson announced he would not run for a second term in his own right in 1968, he was greeted by massive crowds in subsequent public events around the country. Years earlier, in March 1952, Harry S. Truman, another Democratic president, had decided not to seek his own second term.