Aaron Alexis was acting alone when he got inside Building 197 at the Washington Navy Yard and broke out a Remington 870 pump-action shotgun, killing 12 people and wounding three. But others opened the door for him: Alexis gained access to the sprawling compound thanks to the security clearance he had obtained while in the Navy and retained afterward as a military contractor. Alexis' behavior should have led someone to revoke his clearance months ago--but no one was paying attention.
Here is the world's worst-kept secret: the military's security-clearance system is utterly, tragically broken. Army Major Nidal Hasan, armed with a...