"You haven't aged a day."
Joe Biden, 80, couldn't help laughing as he was complimented by Vietnam's 79-year-old Communist Party leader during a visit to Hanoi.
However, the humorous aside was at odds with the constant criticism from home about his advancing years as he campaigns for a second term.
If he is re-elected next year, the Democrat would remain in the White House until the age of 86, a prospect that does not sit well with Americans.
Biden's age is a major handicap in the polls, despite the White House's efforts to boast about his economic, social and diplomatic successes.
Some 73 percent of voters are concerned about his physical and mental competence, while 76 percent doubt his ability to last through a second term in office, according to a poll published by CNN on Thursday.
That didn't stop Nguyen Phu Trong, Vietnam's most powerful leader, from telling the president "he looked better than ever".
"I think you look very young, handsome... you have beautiful white hair," Trong said.
- Stairs -
But journalists who follow the US president have noted the long weekends with his family and the little protocol adjustments he makes.
Public radio station NPR, for example, devoted an entire article to the number of steps the octogenarian climbs to board his plane.
Air Force One has two staircases. American presidents generally take the longer of the two, which takes them to the top of the aircraft, with its excellent vantage point.
But Biden increasingly uses another staircase, shorter and more stable, which is usually used only in bad weather.
The president has already stumbled on the main staircase and he has also fallen in public, once during a bike ride and another time at the end of a speech.
These images were broadcast around the world, much to the delight of the Republican opposition.
At Biden's last medical check-up, in February, his doctor described him as "vigorous" and in "good health", but his age continues to preoccupy voters in a country obsessed with youth.
His gait has become cautious, his speech is sometimes slurred and, with the camera constantly on him, there is nowhere to hide.
By contrast, Biden's Republican predecessor and likely 2024 rival Donald Trump, 77, sees his weight discussed regularly but his age has not yet become an issue.
- Bed, basement -
Biden looked frail as he gave a news conference in Hanoi, telling reporters still trying to ask him questions as it came to an end: "I don't know about you, but I'm going to bed".
He also caused some confusion when, asked about reducing fossil fuels, he embarked on a rambling response that centred on an unidentified John Wayne western film.
The performance will further fuel conservatives who have accused the Democrat of campaigning for the 2024 election from his basement, from where he broadcast numerous videos during the 2020 race at the height of the Covid-19 pandemic.
The White House responded by emphasising the president's very busy schedule as he embarked on a five-day world tour, taking part in the G20 summit in India before arriving in Hanoi.
White House deputy communications director Herbie Ziskend posted the details of Biden's packed itinerary Monday on X, formerly known as Twitter, ranging from meetings in Vietnam to a 9/11 commemoration in Alaska.
"Hanging out in the basement," he quipped.