How can Biden still be President when even his aided admit he is in decline?

Even during this few month lame duck period, we have a President who I have been reading even from left-wing sources that his aides say he "has good days and bad days" and is in "obvious cognitive decline".. and he is still President, wtf? How can the cabinet not remove him?

How can Biden still be President when even his aided admit he is in decline?
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