Update: Sidewalks, Streets, and Tweets: Is Twitter a Public Forum? [Updated July 9, 2019] [open pdf - 658KB]
From the Document: "Update: On July 9, 2019, the U.S. Court of Appeals for the Second Circuit issued a decision affirming the trial court's ruling described below. In its opinion, the appellate court concluded that the President had essentially converted the private @realDonaldTrump Twitter account into a government account by using it for official business. The court further held that the President had opened up the 'interactive space' of that platform as a public forum for purposes of the First Amendment by making the account's 'interactive features accessible to the public without limitation.' Consequently, because the First Amendment prohibits viewpoint discrimination in public forums, the court concluded that the President acted unlawfully when he blocked users from these interactive spaces on the basis of the users' viewpoints."
CRS Legal Sidebar, LSB10141
Congressional Research Service: https://crsreports.congress.gov/