I don't expect that he's lost ANY voters since last time, and there are a lot of people who weren't sure before, but will vote for him this time.
And Biden looks like he's on his last legs. Any of us who have dealt with our parents, aunts, and uncles who had dementia or Altzheimer's know exactly what those symptoms are, and he's got them. And none of his supporters appear to be "excited" about him. Even his Black support (usually 95% + for the Democrat) is falling away.
But that's just my take. We'll know in 4 weeks, I hope .... !