From 538: Biden has consistently polled better than Clinton ever did. It doesn't mean he can't still lose, of course, but he's consistently polled over Trump better than Hillary did even at her peak, and his lowest level of support so far beats Hillary's highest level by some 3.5 points.
https://fivethirtyeight.com/features/biden-is-polling-better-than-clinton-at-her-peak/
https://fivethirtyeight.com/features/biden-is-polling-better-than-clinton-at-her-peak/