"I'm gonna steal the Declaration of Independence"
Imagine being the IT dept at the Capitol Building: every piece of electronic equipment will have to be replaced, even the stuff still in shipping boxes. Agents got physical access to the entire building, workstations were left powered and unlocked when they evacuated. Even if there wasn't gross opsec violations (we saw open inboxes on screens posted to Twitter, for fuck's sake), someone could carry in a keyboard in with a cel modem, leave it in the spare-parts closet, then go back to waving a Trump banner while shouting in a well-practiced American accent.