I remember seeing a few video clips during the primaries from the more hardcore and Extremely Online Bernie folks on Twitter, but I never took them seriously.  Biden's never been the most eloquent speaker, and he has good days and bad days like everybody -- although the range on that has always been pretty wide with Biden (when he's bad he's really bad and when he's good he's really good).

Biden's strongest moments in the debate were the moments in which he was allowed to talk directly to the public, so while those folks may figure Trump made a mistake there, Trump's strategy to try to create a shitshow and muddy the waters probably wasn't a bad one.  But, being Trump and having no self-control, he obviously went overboard with it.

Be nice to America. Or we'll bring democracy to your country.