Reading about this tragedy, the shooter was investigated by the FBI twice- once for an outburst in an office, and a second time for contacting a suicide bomber. He bought his guns legally because he was a licensed security guard who worked in federal buildings. His father was a known vocal supporter of the Taliban.
I do not claim to know what would have been the proper course of action. He is a U.S. Citizen. But it at least appears that political correctness averted more effective action.
A couple more of these and the backlash will be hard to contain. It is already happening in Europe. And while I do not fall for the trope that all Muslims are to blame, it behooves the moderates to very aggressively clean up the support the radicals get from within their Mosque walls.