Hi Euro ATC;
Nope we probably wash about 50% out, but still that leaves us with plenty of folks to chose from. We also wash many who have worked other places. Shoot, we even wash those coming from other facilities in our busier places <G>...
The security clearance isn't for working run of the mill military stuff. It is for working stuff that some other folks don't know anything about <G>.... Also for some law enforcement stuff that goes on that others are probably not privy to.
But, to answer your question, I doubt the US will ever feel that they are hard up enough to change the citizenship requirement. They didn't do it in 81 when they fired most of the controllers working, I doubt that they will do it when they are just a bit short <G>...
regards
Scott