Even with all his health, mind, mental, or other issues, he's as corrupt of a politician as I have seen in my lifetime. He openly brags about using US taxpayer dollars to force Ukraine to not investigate deals his son was involved in. He took his son to China on Air Force 2 and his son comes back with a billion dollars in Chinese financing. Where is that money?
But if were elected anyway, he's clearly an argument for the 25th Amendment. A real one, not the made up one that they made out of Trump. So, not that it will happen that he's the candidate or is elected, but Biden's VP would be who the Democrats actually choose and, if Biden or his people get in the way of his VP running the country, they would Amendment 25 him.