Biden is effectively running opposed as well. There is no real anti-Biden candidate or movement.
The problem leftists/communists/etc will have is that they pulled themselves out of the political process long ago. They didn't vote in 2016 (or voted for Trump). They didn't vote in 2018, 2020, 2022, 2023 special elections etc. Yet they parade around demanding someone earn their vote when the cake has already been baked. We have a general idea of the type of voters who will show up in November for Trump and Biden. It's not gonna be Hasan Piker types.