A short thought experiment: Imagine that walled garden social networks never caught on. Instead, people post things to their personal blogs or use services like Tumblr, Blogger, Flickr, or newer sites that had come along for their thoughts and photos and such. People still have timelines where they read their friends’ posts, but they’re less centralized, backed behind the scenes by RSS, maybe with some extensions to make replying and such work nicely. (Though people don’t need to actually know what RSS is; this is how podcasts have always worked.)
In this setup, when Trump or any other white supremacist posts something, he does it to his own site (whitehouse.gov or trump.edu or whatever). People who follow him still see it in their timeline, but it’s not owned by the same entity that runs the timeline.
The provider of your timeline is just an aggregator. They scrape up posts from your friends and combine them into a timeline for you, but they don’t own the posts; they’re hosted elsewhere. As such, it’s not their problem if someone posts misinformation. It’s that person’s host.
The government could require that anything posted by the president use the official whitehouse.gov feed, which would have associated guidelines and an appropriate understanding of what force of law it’s communicating.
Again, as far as you the user is concerned, you’re still just reading a timeline containing the stuff the people you follow post. We’re just talking about where those posts are hosted, who owns them, and who’s responsible for banning those users who post stuff they deem objectionable.
The difference, I think, would be that instead of having just two social media giants making these decisions, we’d at least have a wider breadth of hosting services in the mix.