My answer is: the Feds (FBI and DEA)
I say so based on facts that in this campaign there is a lot of comedy show done by S.S.G..
These rallies, either for trump or against him, have the purpose to raise his popularity.
What is S.S.G.?
" The FBI Special Support Group , or SSG (They're nicknamed G's), supposedly does much of the routine work for the Bureau, leaving the FBI agents themselves free to pursue more important matters. ...
They usually work part-time, and earn about $5,000.00 - $10,000.00 per year or more. The FBI doesn't advertise the existence of the SSG, but it's no big secret either. The reality of the Special Support Group is much different than the "released" information. SSG teams regularly harass and even menace people on the FBI's Black List. ...
The FBI calls this harassment "dangling," and they do it on a regular basis to people who frequently have committed no offense other than to have drawn the ire of the Bureau. Many SSG's are of the lowest caliber of human life, especially those chosen for excessive harassment of innocent citizens. Far too often SSG teams consist of bullies, perverts, racists and ex-convicts and other dregs whose sole purpose is to drive people crazy and ruin their lives. If one of their victims snaps and tears one of them up, the bloodied G will press charges, perjure himself if confronted with his FBI affiliation, and the victim is locked up. Mission accomplished. That's one reason why the FBI is not very open about the SSG. This is just one of the many questionable and outright illegal activities that the FBI uses our tax dollars for. The very people sworn to uphold our Civil Rights are perhaps the most flagrant violators. If you attend a protest rally, or otherwise call attention to yourself, don't be surprised if you start seeing the same bizarre group of people showing up everywhere you go, bothering you and behaving like psychotic clowns."
Of course, Donald Trump himself is a high ranking S.S.G..
He is chosen because something big and bad will happen. No big group (Democratic Party or Republican Party ) wants to take the responsibility. A clown would easily do that job.