https://techcrunch.com/2018/05/23/its-unconstitutional-for-trump-to-block-people-on-twitter/

A uniquely 21st-century constitutional question received a satisfying answer today from a federal judge: President Trump cannot block people on Twitter, as it constitutes a violation of their First Amendment rights. The court also ruled he must unblock all previously blocked users. “No government official is above the law,” the judge concluded.

The question was brought as part of a suit brought by the Knight First Amendment Institute, which alleged that the official Presidential Twitter feed amounts to a public forum, and that the government barring individuals from participating in it amounted to limiting their right to free speech.