What are the options (if any) when attempting to prevent gun violence by someone who has not yet committed a crime?

This recent post has me revisiting a question I often wonder about:

When there is a mass shooting and we later learn the shooter was showing all kinds of signs of trouble, the question always becomes “why didn’t someone intervene to stop him from doing this.” But, assuming the future shooter was not amenable to any sort of therapy/counseling/other aid suggested by friends or family, is there actually any action one could take in that instance?

Let’s say you’ve got a man who owns a lot of guns, is gainfully employed and appears stable from the outside, but binge drinks every night, screams abuse at his partner, frequents online spaces that encourage paranoia and violence, and maybe even experiences the occasional borderline psychotic episodes common to those with long term alcohol abuse. (An unfortunately not-uncommon character these days.)

But he has never explicitly threatened anyone, never committed any act of physical assault, and does not consume any illegal substances. He refuses to acknowledge any problem or submit to any healthcare or other intervention.

He is clearly a huge potential danger. And were he to suddenly snap and murder his spouse or go on a shooting spree, no one who knew him well would be that surprised. But he hasn’t committed any crime.

This is when everyone asks “why didn’t someone do something?!” But realistically, is there anything one could do?