vote share * turnout

Reagan 1984: 53.3*58.8= 31.3%
W Bush 2004: 50.7*56.7=28.7%
Obama 2008: 52.9*58.2=30.8%

Biden 2020, estimated: 51*66 = 33.7%
counted so far: 50.5*60.3=30.4%

If trends hold up-- and remember that besides swing states, there's still millions of votes left elsewhere (c. 4 million in California & New York alone)-- Biden voters were a historically large share of the population, rivalling or maybe beating Nixon 1972 (33.5%).

This was not an election marked by low Democratic enthusiasm or turnout or motivation. If your "no Democratic ground game" or "no minority voter enthusiasm" or "too much campaigning from the basement" or "Bernie/ Warren would have excited people" theory says it was, revise it.

Currently counted: 61.4% turnout * 50.5% vote share = 31.0%.