Webb lives in Virginia.
What happened with Webb is a problem I've often considered, as have many who have live in Virginia and have concealed carry permits.
If your job takes you into DC your permit is pretty much useless. Because 5 days of 7 you'll be leaving your firearm at home to comply with the DC gun ban. You really don't even want to transit through DC or to park your car and leave your gun there while working unless you want to test DC's non-recognition of "peaceable journey" provisions ("peaceable journey" is recognized by federal law, DC law is silent on it).
OK, I can live with that (BTW, I don't work in DC and don't carry regularly anyway, this is hypothetical), but what about the Northern Virginia woman who's being stalked, or who's been raped on her walk home for a Virginia Metro stop, or the guy who's been robbed? All of those people really can't carry during the week when they work in DC.
Fine, "Tell them to get jobs in Virginia".
OK, let's say they all do get jobs in Virginia. Now they can carry, and leave their firearm tucked away in the car while working. Problem is that many Northern Virginia workers might have cause to drive into DC one day, or to go into Maryland via DC interstate highways.
Once again you're screwed. Because the moment you cross the Potomac you're theoretically in violation of DC's silence on peaceable journey. You're in (almost) the same position as Webb's aide.
Or consider the delivery truck driver with a permit. You might have your firewarm secured in conformance with standard peacable journey requirements, but once you set tire on a DC street, once again you're screwed.
Back to Webb's aide.
Since he had a permit, there was no violation of Virginia law. Once he crossed the Potomac that was no longer true. And for the next 10,500 feet that remained the case. But the moment he drove on to Congressional property he was covered by Senate rules which allow Senate members and their staff to "transport" a fiream (which makes me wonder why DC is even involved in this, since the Senate rules are fairly clear).
I could be wrong, but I don't think DC has any case so long as he was "caught" on Senate grounds. What's left is the presumed 10,500 foot drive from the Potomac River to Senate property, all of which would likely have happened on I-395, a federal interstate