It's like that sometimes. After a certain age, the stairs can even become a serious opponent.
We already knew that the Democratic president of the United States is sometimes... well, a little wrong. There are times when he believes he discovers his deceased son in his granddaughter (of course, in the USA it is already considered a crime to name whether it is a boy or a girl), sometimes he is not sure whether he or Kamala Harris is the president, but to err is human, isn't it ?
To stumble as well. It's true, three times in a row seems a bit much, but the White House spokesman also explained that: the wind was to blame. (He could have said that Biden's shoes, or even the stairs, is at least as credible a statement.)
But it's a shame to make fun of this, because we know that a horse has four legs, but it still stumbles. Biden only has two.