It helped him alot and it will help Biden as well.
Incumbency Advantage in U.S. Presidential Elections: The Historical Record
DAVID R. MAYHEW
....
I want to argue here that incumbency advantage in the statistical sense, underpinned by a corresponding mix of at least promising causal factors, is a good candidate for an account of American presidential elections. Other current scholarship has been pointing this way. Herbert F. Weisberg, drawing on a study of pooled individual survey responses for elections from 1952 through 2000, reports that incumbent presidential candidates enjoyed a bonus of 6 percent in the popular vote. Ray C. Fair, using aggregate data for elections from 1916 through 1996, reports a bonus of 4 percent. David Samuels, using aggregate data in an analysis of presidential elections in 23 countries including the United States, reports a bonus of over 8 percent.
https://www.jstor.org/stable/20203009
