What do you get with someone who is a devout Muslim with tenuous links to ISIS that have been investigated by the FBI, who has mental health issues and engages in abusive behavior, and who regularly makes racist and homophobic statements? The worst mass killing in U.S. history? Maybe. Or you might get nothing. That’s the problem. Without more to go on, there’s no way to predict what might happen. Now add one more factor: that person buys a semi-automatic weapon and a shit-ton of ammo. You’d think that might raise a flag, but it didn’t. Whose fault is that?