You can ban guns...but you can’t ban crazy homicidal maniacs.
IMO, you said it all right there.
As this implies, it covers the gunman, the Left in general, and the gun banners.
According to Krauthammer, Connecticut has the fourth most stringent gun control laws of any state. This should have made it impossible for the violence at the school to take place.
Gun laws don't work. They merely make victims of those without guns.