As Andrew Gelman showed with the Obama/Romney debate, pretty much all of Obama's apparent poll decline after his bad debate was just partisan non-response.
Gelman adjusted for it (the dark line) and there was very little movement in the race.
Fwiw, most everything I'm seeing is a small Biden decline nationally and in swing states on average. Not great obviously as he was already behind. It makes sense as his debate was atrocious.