The one thing you can guarantee is that any competent terrorist group is going to be able to get around this kind of stuff. Not exactly difficult.

It seems pretty obvious that the purpose of this is nothing to do with actually reducing the risk of terrorist activity, it's about bureaucrats protecing their own backs. When there is another big terrorist atrocity in the States, likely enough by someone who has been living there all their lives, the idea is to be able to give a great list of "precautions" that had been carried out.

Maybe we'll get back to the old days when American musicians weren't generally able to perform in England, and I imagine the other way round for the States. That had some good consequences at times actually, and a lot of musicians here owed their professional careers to that situation.