From all I have heard the shooter was nuts. There are a lot of questions but this one will probably be nailed down to nothing other than mental illness however:
How would his mental illness have manifested itself without the Glen Becks and our political climate?
I think you've hit the nail on the head. Talking about "watering the tree of liberty" and "second amendment remedies" and "I want (my constituents) armed and dangerous." Is lighting a fire that burns indiscriminately.