Violence is increasing at Trump rallies, where he creates an atmosphere of anger and animosity toward protesters and the media. As a result, people exercising their First Amendment rights are being injured.
He incites violence with comments like those documented by the Washington Post at:
https://www.washingtonpost.com/news/the-fix/wp/2016/03/11/could-donald-t...
In Brandenburg v. Ohio, the US Supreme Court found that inflammatory speech may be prosecuted if it has the intent and likelihood of imminently inciting lawless action. Trump speaks to the intent, the hostile atmosphere and track record of his rallies establish likelihood, and the presence of riled supporters and targeted protesters establish imminence.