Yet another mass shooting, and flags fly across the country at half-mast to mourn the 13 dead at the Washington Navy Yard—well, 12 of them, anyway, since one of the bodies was that of the murderer. Gun control advocates wasted no time in demanding new restrictions on the means of self-defense. Sen. Diane Feinstein (D-CA), who used to carry a pistol for her own defense, responded to the crime by saying, "Congress must stop shirking its responsibility and resume a thoughtful debate on gun violence in this country. We must do more to stop this endless loss of life." But the unhappy truth is that the scene of the crime, the Washington Navy Yard, is subject to many of the restrictions that gun control advocates favor. And the perpetrator, Aaron Alexis, had passed a background check for a security clearance. Unfortunately, laws and databases don't create magic forcefields against criminal intent.