that is not how dementia works.
You have good days and bad days, and the bad ones get longer and come more often until it is nothing but bad days.
It is a steady decline that accelerates near the end and nothing can stop or prevent it from happening once it starts.
I remember Nancy having to feed answers to Ronald and the left screamed and no one else. It’s not at a cease-to-function stage.
No reason he has to resign. The best thing for the country is a Trump presidency and that is best served with Biden remaining where he is.