(AFP) - Joe Biden will complete a routine medical checkup on Thursday, a crucial step for the oldest-ever US president ahead of his expected fight for reelection in 2024.

The White House has promised to release the report by the 80-year-old president's doctor, as it also did during his previous checkup in 2021.

This time around, with the Republican 2024 campaign already kicking off, it will be scrutinized even more closely.

Despite poor poll ratings, Biden -- a Democrat -- has been suggesting for some time that he intends to run again, potentially lining up a rematch of his 2020 battle with his predecessor Donald Trump, who has already declared his candidacy.

"That's my intention, I think, but I haven't made that decision firmly yet," he said in a PBS interview on February 8.

Biden's last checkup was on November 19, 2021, when he underwent a complete examination, including a colonoscopy under general anesthesia.

He transferred his powers for one hour and 25 minutes to Vice President Kamala Harris, making her the first woman in US history to hold the presidential prerogative.

Biden's doctor, Kevin O'Connor, at the time painted a picture of a healthy man fit to carry out his presidential duties.

But he did also point out relatively minor signs of old age, and noted Biden's stiffer gait, attributing it to a mild nerve condition affecting the feet; as well as a frequent cough caused by gastroesophageal reflux.

Biden does not smoke, does not drink, plays sports, and has not had any major health concerns since undergoing brain surgery in 1988.

He tested positive for Covid-19 last July, but did not have a serious form of the disease.

The American president has shown uncommon stamina, making public appearances and travelling.

But his age remains a frequent angle of attack by the Republican opposition.

Some of the president's opponents even claim that he is no longer in his right mind, citing some of his moments of confusion and his slurred speech. Biden has spoken often of overcoming a childhood stutter.

Nikki Haley, a 51-year-old Republican who has just entered the race for 2024, called Wednesday for mental fitness tests for any elected official over 75.

That would also apply to ex-president Trump, 76, whom she is challenging with her candidacy.

Haley, a former UN ambassador, hopes to capitalize on the American electorate's desire for fresh blood in politics. Polls show many do not want a second Biden term any more than they want a repeat Trump presidency.

If he runs, Biden will have to face both the rigors of an election campaign and the demands of his office.

He wants Americans to judge him on his results, effectively saying age is just a number.

"Watch me," he likes to say.

© Agence France-Presse