Not true.
The radical left will vote for Biden et al regardless of what he says in debates or campaign speeches.
Most will, but it's very possible some of them might realize that he just says whatever he thinks people want to hear at that moment, and will be put off by him. Trump clearly thinks it's possible to peel off some of Biden's left wing support.
Not true, many didn’t vote for Hillary the last time and even more won’t this time.