WASHINGTON -- U.S. President Joe Biden had a routine medical checkup Thursday at Walter Reed National Military Medical Center, a keenly watched exam as the oldest president in history makes plans for an expected reelection campaign.

Biden was at the hospital in Bethesda, Maryland, for about three hours before leaving by helicopter shortly after noon for the White House. The White House was expected to release a letter later Thursday that would discuss the results.

Biden, 80, last had a standard medical exam in November 2021. During that five-hour-plus visit, he went through a combination of blood, physical, gastrointestinal, dental, vision and neurological tests. Afterward, Dr. Kevin O'Connor, Biden's primary care physician since 2009, signed a six-page memo that called Biden "healthy, vigorous," and deemed him "fit to successfully execute the duties of the Presidency."

Many people, including Democrats, have expressed reservations about Biden seeking a second term in 2024. Only 37% of Democrats say Biden should pursue reelection, down from 52% before last November's elections, according to a recent poll from The Associated Press-NORC Center for Public Affairs Research. Overall, 22% of U.S. adults said he ought to run again.

Follow-up interviews with people in the survey indicated that Biden's age was a major concern. They took note of his coughing, a greater sense of fragility in his walking and moments when he misspoke.

During Biden's 2021 physical, a neurological exam found nerve damage to his hands and feet that had contributed to his stiffened gait. Spinal arthritis and compensation for a broken foot also caused him to walk more cautiously.

Biden had a colonoscopy in 2021, in which a 3 millimetre "benign-appearing polyp" was identified and removed.

Asked in a recent PBS interview about his age and ability to be president, Biden responded with what has become his stock line: "Watch me. It's all I can say."

Biden tested positive in July for COVID-19 and experienced "very mild symptoms," according to the White House. The president continued to work even as he isolated himself in the White House.