In Davison v. Randall, a local government official in Virginia blocked a constituent from her “official” Facebook page. The court held this to be viewpoint discrimination.
The ACLU and the Knight Institute then argued that Donald Trump cannot block people on his Twitter feed. Lower courts have agreed.
The ACLU is likely to prevail against Trump, but the problem is, the courts have allowed Facebook and others to do exactly the same thing on a much larger scale against ordinary people.