Curious: Why would this fall under the cognizance of the Secret Service? FBI or DHS, I could understand. Please enlighten me.
I think it is pretty straightforward: It is a threat. Pure and simple.
Before the Internet, people would say things like “The President deserves to be shot” and someone hearing them would report it, and it would end up with the Secret Service who would investigate. People wrote letters to newspapers and the President himself saying things like that and would get investigated.
It is the job of the Secret Service. With the Internet, it is a tsunami of stupidity, but...they have to investigate where they can.