Sorry, Doc. If Kilborn was not arrested, they did not do anything. Case closed.
Did you expect an arrest? Did you expect he'd get a visit?
I'd bet he was interviewed, probably others involved with it too. The USSS have to determine if it's a wise ass with a poor attitude or something more.
Unless it's specific as to where, when and how, unfortunately isn't "legally" a threat, so no arrest.
Personally, my initial reaction is I'd like to see things like that shirt be a misdemenor. Mainly because there are enough degranged liberals out there who could mistake that "protest" for reality and act out.