We don't know what this is yet. That said, ISIL has said they will target the US. Muslim extremists hit Paris, - a place with an unarmed general population. There is practically an unlimited quantity of small arms in the world; it is an impossible task to control their movement by those willing to smuggle them. Our borders are porous and this administration wants to allow more people in from the ME who have not been vetted.
Do any of these facts lead one to conclude that its a good idea to disarm law abiding Americans because of the actions of nut cases or jihadists ?
I don't think so.
P.S. - if jihadi types, they will try to down play it. If white guy nut (on psych drugs) - they will play it up to the max.