I hate to pile on here, but...
I've heard interviews of some of the original air marshalls (1970s), and they were the most elite and hand-picked of all federal law enforcement officers. They were the best in the world.
Nowdays, it seems like the standards are definitely slipping. Air marshalls in the past didn't fall asleep on the job, or get in fights with flight crewmembers, or leave their guns in the lavatory to be found by other passengers. Evidently they are able to pass the qualifications of the day, though.
And I still can't take my Leatherman with me, 'cause I might take control of the plane. Pathetic.