Re: Be afraid, be very afraid ... of the wrong thing.
As it happens,I have that experiece: I flew into Denver about two weeks after 9/11 and, because I'm a glider pilot and intended to fly gliders in the USA, I had my UK log book and license documentation with me.
The procedure for getting a US ticket was to visit the appropriate office (that was Denver for me, since I was visiting friends there and intended to validate my US licnce, when issued, at Boulder. Getting into the Denver CAA office was scary, since I was to be escorted to the relevant desk by a heavily armed door guard, who took me to the appropriate desk and then left. The surprise was that, US licence issued, I was than left to find my own way out when I'd expected to be escorted out as well, and so was never checked out. Sloppy security or what?
Paperwork issued, I drove to Boulder airport for check flights to validate my new US license. This involved aero towed launches in a Grob G103: (no huhu as my UK club had one ands I was already solo on type) and, a few days later, ended up it it at 17,000 on oxygen over downtown Boulder: fun! Subsequently, I flew flew other gliders in CA at Williams and Minden and got a type conversion to the Pegasus 103 at Williams - worth while as my UK club has one and I intended to fly it.