It's perfectly legal to advocate murdering your political enemies. See, Brandenburg v. Ohio. Since you can't actually kill someone over the internet, anything you say online automatically fails the "imminent lawless action" test. LEOs can't do anything about speech unless "speech is brigaded with action".

Gas all liberals, CIVIL WAR NOW!!!! The day of the rope for all you cucks and libtards is coming soon and I can't wait!!!1!!!! Just to be clear here, I want libtards lynched in the fvcking street by a large group of people, not some lone nut shooting. Day of the rope will be here sooner than you think as this idea spreads. Instead of worrying about trying to lock people up for their political views, why not just not be such a horrible scumbag so that people don't want to kill you for your abhorrent political views?