So some of you folks are suggesting that secrecy is a solution to some of these problems? You could probably find some good advisors from Germany or North Korea, maybe even China (a preferred trading partner). In other words, we just keep these things hushed up.
One little problem here with suggestions that criminals don't obey laws is that this fellow wasn't a criminal, as far as I know, until he started pulling the trigger. So the problem is keeping people from becoming criminals in the first place, though I have no idea what might work. All of things about background checks and so on might work but I expect everyone here would object just the same. But if he wasn't a criminal in the first place....
More security? Like metal detectors, frisking and so on? That would presumably eliminate the legally armed individual. In some places they don't let people with the wrong bumper stickers go to political rallies (which this wasn't) and in a way, I guess that works, too. Sort of benign way of eliminating the opposition.
I am sure, however, that everyone in congress is concerned, not to mention every other elected official and probably most appointed officials, like judges. Judges already have their hands full with threats from certified and convicted criminals, must less from people who just don't like them. But remember, people in office were elected. That means more of the voters wanted them in office than the other person. If someone thinks that they feel justified in making threats or worse to an elected office holder, and it happens, well, then, that bothers me.