I think that Biden has done wonderful things as president, despite the adversity of a very divided Congress. I think it likely he is still competent to execute most of his duties. But one part of his job (maybe the only one that Trump works at) is projecting the image of being in control and competent. Biden failed at this in the debate.

It wasn't just a 90 minute lapse. It wasn't a pop quiz, this was an extremely important mid-term exam, announced weeks in advance. It was his job, assisted by his aides and doctors, to be ready for that exam, and perform at his best .

I've explored issues related to his ADHD, aging, and Parkinson's in greater detail here: https://medium.com/p/7192a2af6a1b