Estimated 600 there. I have already written about his difficulty finding words he wants to say. People will vote for him for who he is, not what he says. It may go like this: If he is their nominee, the crude words Trump will use calling Biden names, will give poor/sweet Biden more votes. - did you know his son died of brain cancer some months ago and wanted him to run for president? Vote for Biden for his son's wish to come true. Biden is nicer than Trump - vote for Biden.
For real, it is likely Biden can't keep up the pace. I think he will have to quit. His family should know he is too frail. He has never been a good public speaker and he is poor at that now.