I am going to ignore the rest of your post and use this specific aspect to highlight something. Joe Biden has had a stutter his entire life. Stutters take an extensive and persistent amount of work to overcome. They are likely to return during times of increased stress, decreased sleep, or when one ages. There is zero evidence that Biden has experienced any kind of mental decline. All the evidence that people point to of him stumbling over his words, calling someone by the wrong title, or whatever other examples you have are almost certainly just symptoms and coping mechanisms used by someone with a stutter.