Let's see who wins the nomination in 2020 for the Democrats. Don't forget the Republican establishment didn't want Trump either. This is all a fairly recent change.... it used to be both parties would quiet the more radical members..... but not so much anymore. Even Pelosi has been receiving a lot of blow back for trying to move to the center (who would ever thing Pelosi would be center). What I will say is we KNOW the Republican establishment will bend to the will of Trump if it means electoral success, even if it means altering some core issues and beliefs....... We don't know that the Democrats would end up doing that, but we will see, depending on 2020.
The democratic base is trying to elect Biden though. Much to the chagrin of people like @glynch , the Democratic base is much more moderate. You are right though have to see who gets nomination.
You have it backwards. 4/8chan are cesspools where no counter balance exists. Otherwise rational people in it for the lulz go to places like that and end up in an echo chamber of terrible ideas, terrible information, terrible sentiment, and terrible motives. Nobody who goes in comes out better off for it. YouTube and other social media, on the other hand, are tools for open discourse and dissent. It's arena of ideas and there are plenty of counter points being made. For every radical who gets sucked into the vortex of borderline white nationalist garbage there, there's another person who gets deprogrammed by the same exact platform.