Sorry, to clarify, I meant a nation-wide increase in mental health research\awareness, with the specific intent on locating individuals who are in need of mental 'medical' attention, in the same way we do for physical and (arguably) spiritual wellness. In theory, this could have 'teased out' whatever it was that was going on in this person's head which give this particular person a proclivity toward violence, and either treat it or at least prevent them from obtain a weapon, while not limiting the rights of citizens who aren't prone to this kind of behavior.
Mind you, I expect this to be a rather expensive, and long-term endeavor, not something that happens overnight. I also think it's a solid way of approaching this issue without trodding over the rights of citizens, and as a bonus, it could put the US front-and-center on something again, with dramatic advancements in understanding the human mind and furthering our species' knowledge of how our brains work.