The idea that we can do something to prevent this from happening again is fantasyland. Even the idea that we can do something to make it less likely is dubious at best.
On the left we must be rational in any political reaction to this tragedy. First if anyone is calling for handguns to be made illegal, that would be an asinine and utterly hopeless lost cause. It's some sort of desperate grasping for some grand final political victory over the right wing in the gun matter. It ain't ever going to happen. Period.
What we are dealing with here is a human mind snapping in an environment where a negligent dimwit (alleged head of the household) had guns that were known about and easily accessible. And, unless they were a total moron (which is a distinct possibility), had to have at least suspected to some degree that there was a person present with some problems. I'd very much like to hear, and respond to, any legislative proposals to prevent this.
Other than, of course, the hopeless making of guns illegal for everyone.