Joe Biden's advisers knew in 2020 that his age was an issue for Americans but they successfully painted him as a competent leader who would restore normalcy to the White House after Donald Trump's chaotic presidency.

Now that Biden is 81, opinion polls show age is even more of a concern for voters ahead of November's election.

In office, Biden's gait has stiffened, he is slower on his feet and he regularly makes verbal mix-ups during speeches, at times confusing the names of world leaders.