President Biden acknowledged that he may not have had the stamina to serve another four years in the White House if he had won reelection. "I don't know," Mr. Biden said in a recent interview with USA Today when asked whether he "would've had the vigor to serve another four years in office.

President Biden insisted that he still could have beaten Donald J. Trump had he stayed in the race, but could not say he would have been vital enough to be president until age 86.