The Technology 202: Biden targets Zuckerberg as his campaign mounts a Facebook ad blitz - The Washington Post
Trump is feuding with Twitter, Biden is feuding with Facebook, which is exactly what the fuss about Section 230 of the Communications Decency Act is about. Section 230 protects online content platforms like Twitter and Facebook from, with certain specific exceptions, being sued over content posted by users. Conservatives hate Section 230 because they contend it results in too much censorship, which they feel is unfairly directed at them (e.g., by Twitter); liberals hate Section 230 because the feel it results in too little censorship, giving voice to opinions they disapprove of (e.g., by Facebook, as above).
Here's more, from EFF: