The disclaimers can be disregarded. All the government needs to do is to issue a directive that anyone known or suspected of suffering from a mental disorder as defined by the DSM-V is prohibited from owning or possessing a firearm.
That would include everyone.
Congress too because the DSM includes substance use disorders too :) Seriously, if the real focus of this effort is to deal with mentally ill people with a potential for violence, then those people need to be adjudicated mentally ill, not simply diagnosed based on criteria which the DSM itself admits are insufficient proof of mental disorder. There needs to be a hearing with legal counsel and a judge. And reports, testimony, etc. Anything less is a disregard for our constitutional rights.