> Especially if they can just slip the janitor $10,000 to put a USB labelled "Barely Legal Gone Wild" into the machine while vaccumming.

Part of Defensive Depth includes vetting and requiring the janitor who cleans the SCIF to themselves also hold a security clearance.

Your cited example is also why Counterintelligence is a thing. It's not enough to trust your processes; you also have to probe them.

When I was in the military I met a guy whose job was to pentest (among other things) nuclear weapons facilities and NORAD defense installations, specifically their computer equipment. He had some pretty wild stories; suffice it to say the ladder trick doesn't work when you are trying to access an ICBM solo.