From Knight First Amendment Institute at Columbia University v. Trump, 2019 WL 2932440 (2d CIr. July 9, 2019):
Considering the interactive features, the speech in question is that of multiple individuals, not just the President or that of the government. When a Twitter user posts a reply to one of the President’s tweets, the message is identified as coming from that user, not from the President. There is no record evidence, and the government does not argue, that the President has attempted to exercise any control over the messages of others, except to the extent he has blocked some persons expressing viewpoints he finds distasteful. The contents of retweets, replies, likes, and mentions are controlled by the user who generates them and not by the President, except to the extent he attempts to do so by blocking. Accordingly, while the President’s tweets can accurately be described as government speech, the retweets, replies, and likes of other users in response to his tweets are not government speech under any formulation. The Supreme Court has described the government speech doctrine as “susceptible to dangerous misuse.” Matal, 137 S. Ct. at 1758. It has urged “great caution” to prevent the government from “silenc[ing] or muffl[ing] the expression of disfavored viewpoints” under the guise of the government speech doctrine. Id. Extension of the doctrine in the way urged by President Trump would produce precisely this result.
The irony in all of this is that we write at a time in the history of this nation when the conduct of our government and its officials is subject to wide–open, robust debate. This debate encompasses an extraordinarily broad range of ideas and viewpoints and generates a level of passion and intensity the likes of which have rarely been seen. This debate, as uncomfortable and as unpleasant as it frequently may be, is nonetheless a good thing. In resolving this appeal, we remind the litigants and the public that if the First Amendment means anything, it means that the best response to disfavored speech on matters of public concern is more speech, not less.