Biden is visibly in mental decline; it’s not just Republicans who had said so. He seems unsure of himself when he speaks, makes more gaffes thab when he was younger, and only accepts pre screened questions from staff. He has very low energy, but average or perhaps even above average for a person his age.
I agree that conservatives tend to upplay his condition, saying that he has full on dementia or belongs in a nursing home; i don’t see that. But i do not see a person with sharp faculties either.
Trump, however, is full of energy; whether you like him and his policies or not, he talks just as sharp as he did 20 years ago.