My understanding is, under the precedent set by Brandenburg v. Ohio, the example you give is considered protected speech. "Anyone who murders politician X this

My understanding is, under the precedent set by Brandenburg v. Ohio, the example you give is considered protected speech. "Anyone who murders politician X this Friday, at 4PM EST when he plans to be at this adress, would be a true patriot" is not protected, however; it goes beyond opinion to actual planning of an imminent illegal act.