That's the job of the Constitution, as the SCOTUS made clear in Brandenburg v. Ohio, in which an actual KKK leader was being charged after participating in an armed rally and talked about getting revenge on various races and on those who supported them, like the President and Congress:

"(..) the constitutional guarantees of free speech and free press do not permit a State to forbid or proscribe advocacy of the use of force or of law violation except where such advocacy is directed to inciting or producing imminent lawless action and is likely to incite or produce such action."