Funny, but I always thought that as Americans, we are the real militia and our best weapon against any enemy. We are all responsible for security and "Homeland Defense".
I currently work out of the U.S. and our one flight a week that originates in the U.S., had 2 armed U.S. Marshalls on board. Funny thing, it's a commercial carrier that is contracted to fly military and U.S. Government contractors. One wouldn't think that there would be to much of a hijack threat with those types of passengers.