The National Instant Criminal Background Check System (NICS) depends on state provided mental health information in order to identify persons prohibited from purchasing a firearm. Federal law don't require states to provide mental health records to any agency that performs background checks. Therefore, loopholes in background checks have allowed "mental defective" individuals to obtain firearms.
The U.S. Department of Transportation requires mandatory physical qualifications for drivers of commercial motor vehicles (§ 391.41). A physically qualified person receives a certificate from a medical examiner that is valid for 24 months.
A mandatory mental health qualification certificate could close loopholes in background checks and avoid dangerous individuals from purchasing firearms.