Favorability for the party nominees on election day 2016, per RCP averages:
— David Weigel (@daveweigel) April 9, 2020
Trump: -21%
Clinton: -13%
Favorability now:
Trump: -9%
Biden: -1%
Both candidates start the general with lower negatives than last time, but Biden being basically 50-50 explains why he keeps leading.