I'm sure someone already mentioned this, but Biden winning Georgia, Pennsylvania, and Wisconsin narrowly and Michigan by a larger but still small margin shows he made the right choice with Kamala Harris. It isn't only about her, but taking a chance on high African-American turnout was the winning bet over any other option.
Kamala did bring some life into his campaign because, to be honest, Trump was a workhorse despite the pandemic forcing people inside and out in the streets encouraging people to vote and attending rallies. Times have changed when a candidate could campaign from their porch and out perform their rivals in a election.
