The nation’s oldest serving president at 80 had been greeting each of the graduates at the front of the stage with salutes and handshakes, and turned to jog back toward his seat when he fell.

United States President Joe Biden tripped on a sandbag and fell onstage Thursday while handing out diplomas at a graduation ceremony for the US Air Force Academy in Colorado.

Biden, who is the nation’s oldest serving president at 80, had been greeting each of the 921 graduating cadets at the front of the stage with salutes and handshakes, and turned to jog back toward his seat when he fell.

He was helped back up to his feet and appeared to be unhurt, walking without assistance to his seat in the stands. He was later seen smiling and jogging toward his vehicle at the ceremony’s conclusion.

“I got sandbagged,” the smiling president, who didn’t respond to questions about the episode as he departed Colorado, told reporters when he arrived back at the White House Thursday evening.

“He’s fine,” White House communications director Ben LaBolt tweeted after the incident. “There was a sandbag on stage while he was shaking hands.”

Biden has been dogged by questions about his age and his fitness to serve, and his missteps have become fodder for political rivals as he campaigns for a second term in 2024. He’s had previous stumbles in public, including falling to the ground during a bike ride in Delaware last year. He has also slipped on the stairs while boarding Air Force One.

Former President Donald Trump, the Republican frontrunner to face Biden in the 2024 White House election, reacted to the latest fall from a campaign event in Iowa, saying: “The whole thing is crazy”.

“I hope he wasn’t hurt,” the 76-year-old who has often poked fun at Biden’s age said. “That’s not inspiring.”

“You got to be careful about that because you don’t - you don’t want that. Even if you have to tiptoe down the ramp,” added Trump, apparently referring to his own careful walk off a stage that made headlines in 2020.

Despite his previous stumbles, Biden’s doctor has said the president is physically fit to serve in office. He “remains a healthy, vigorous 80-year-old male, who is fit to successfully execute the duties of the Presidency.” Dr. Kevin O’Connor said after Biden’s most recent physical exam in February.

O’Connor has also examined the president’s stiff gait, saying it was the result of spinal arthritis, a previously broken foot, and neuropathy in Biden's feet.