That horse already left the wide-open barn door.
Those adjudicated mentally defective and anyone who has ever been committed to a mental institution are already in the prohibited persons category, and have been for years.
As imprecise as this wording is, it's just a result of laziness on the part of journalists.
If the gun banners want to block purchase by anyone suspected to be mentally ill, or who is prescribed antidepressants, or who wants to buy guns, they're going to have to try to change the law.
Aye, which is what they are probably attempting to address now.
The way the VA Tech nutcase was telegraphing his psychosis for years, and the enabling "understanding" he was met with time and again by the "authorities", lead me to believe that even if enacted, this law would find little enforcement. For fear of lawsuits, not to mention that it might impact the little darling's feelings...