I wonder if this is a crime. It sounds like criminal solicitation, but I can only find a federal law for solicitation to commit a crime of violence [it appears to have taken place on federal land]. Regardless, the Capitol Police should still be made aware of what is going on.
Send one to the Capitol Police. Even if it is not a crime, they will likely approach this person if they see him. Never know…might get lucky and he has a little meth on him or something.