From the introduction to Sidewalks, Streets, and Tweets: Is Twitter a Public Forum? (LSB10141, May 30, 2018):
On May 23, 2018, a federal district court in New York in Knight First Amendment Institute v. Trump held that the Free Speech Clause of the First Amendment prohibited President Trump from blocking Twitter users solely based on those users’ expression of their political views. In so doing, the court weighed in on the now-familiar but rapidly evolving debate over when an online forum qualifies as a “public forum” entitled to special consideration under the First Amendment. Significantly, the district court concluded that “the interactive space for replies and retweets created by each tweet sent by the @realDonaldTrump account” should be considered a “designated public forum” where the protections of the First Amendment apply. This ruling is limited to the @realDonaldTrump Twitter account but implicates a number of larger legal issues, including when a social media account is operated by the government rather than by a private citizen, and when the government has opened up that social media account as a forum for private speech. The ability of public officials to restrict private speech on Twitter may be of particular interest to Congress, given that almost all Members now have a Twitter account.