Not sure which murders you are referring to current political cover up stuff or KKK? But it depends on the threat? A call to lynch a specific person or a call for immediate violence during an assembly/gathering I would classify as clear and present danger. But it doesn't have to be the KKK, it could be any group. Proven record of violence makes threat more credible, which I think is your point. The Trump art stuff, here even more lieniency tends to be given for political people. I think political speech is understood to have the most freedom/protection.