"God who gave us life gave us liberty. And can the liberties of a nation be thought secure when we have removed their only firm basis, a conviction in the minds of the people that these liberties are a gift from God? That they are not to be violated but with his wrath? Indeed, I tremble for my country when I reflect that God is just; that His justice will not sleep forever. (Thomas Jefferson, Notes on Virginia, 1781)

The other common thread running through all of these mass shootings is, the shooter was mentally unstable. The families which raised these depraved creatures were not particularly spiritual or religious. It could be fair to say that these families were ambivalent about God and that there was not a "conviction" that His hand is guiding us.
Mentally challenged people have been with us since the dawn of time. The major difference between the present and the past is the communities, culture, the Nation in which we live. We have turned our backs on God. We have exchanged our religiously held beliefs for a secular world of materialism and drifting morality. Some may argue that secular people have the same moral values as relgious people but where is the foundation for that secular morality if after traveling down the train of thought it is discovered that life has no meaning?
The "progressive" politicians are going to call for gun control measures aimed at disarming the honest citizen. Because,"people don't kill people, guns do."
The "progressive" doctors are going to advocate creating a massive "State" run mental health system to help the mentally handicapped but mostly to get them off the street, because, "We're the experts and we know what is good for you."
The people need to once again develop the conviction that we are under the hand of devine providence. We all, as a nation need to turn our backs on this secular progressive cancer that has been systematically devouring our institutions, our families, and our souls. We need to go back to church, any church and inculcate our children in the belief that their is a divine creator, he loves us and wants us to be happy, and the pursuit of happiness begins by following the moral laws laid down with our creation. We need to remove from our lives T.V. and violent video games that rewire the mentally/spiritualy ambiguous into stone cold killers.
No laws need to be passed. No new regulations implemented. We the people can implement this idea with our feet. As a Nation, we may not believe in God, but he certainly believes in us and His justice will not sleep forever.