I ran across an article detailing a serious link between two social phenomena, both of which used to be rare. But when one began to increase, so did the other, with a lag of a few years.
The first is non-institutionalization of late teen and early to mid twenties males with schizophrenia and some other severe mental disorders. Now, if blame can be pinned on the 'first mover', this has to be plopped at the feet of none other than Ronald Reagan (himself a schizophrenic sort of president, with some brilliant foreign policy and absolutely bizarre domestic), the one who got government to agree that not taking care of people is the best way to take care of them. So lots of mentally unstable young men were left to wander the streets, cling to families because they couldn't deal with the world, and turn a few jails in the United States into the world's largest de facto mental institutions.
That's sad in itself; if we are a people, it behooves us to take care of "the least" among us, besides the fact that it makes good practical sense to care for such folks so they don't make a mess of the country for the rest of us. But it's truly tragic because of the very strong link to the other social phenomenon in question.
And if we stick to the 'first mover' proposition, then it's entirely legitimate to lay the blame for the increase in mass shootings in America at the feet of Ronald Reagan.