It's not social media. This is the culmination of decades of work, stretching back to the late 1970s. The GOP has been deliberately working towards this moment since Nixon was forced to resign under popular/political pressure. In response they crafted a deliberate strategy to produce rabble isolated from independent factual media, and induct their supporters into a pliable cult free of independent thought, which could then exert pressure against any potential ethical standards of their elected representatives.
2/3 of the House GOP is now firmly in the sedition caucus, including the minority leader, not to mention the several who are out-and-proud QAnon conspiracy nutters. 45% of GOP voters think that the assault on the capitol was a good thing. A large majority are convinced that Trump rightfully won the election.
Plenty of people were radicalized long before social media, e.g. my grandpa who spent his last couple decades religiously listening to Limbaugh on the radio, and later watching O'Reilly & al. on TV. Facebook is another amplifier here, but not the primary source.