David M. Perry is a journalist and historian. He's the senior academic adviser to the History Department at the University of Minnesota. Follow him on Twitter. The views expressed here are those of the author. View more opinion articles on CNN.

(CNN) On his way to a rally in New Hampshire on Thursday, Donald Trump unveiled his latest musing — to incarcerate the vulnerable. This time, he's coming for people with mental illness, suggesting that the United States build more mental institutions because of mass shooters. Worse, it's all too possible some Democrats are going to help him round us up.

David M. Perry

Standing before his helicopter, Trump told the press, "We're looking at the whole gun situation. These people are mentally ill, and nobody talks about that. I think we have to start building institutions again, because you know, if you look at the '60s and the '70s, so many of these institutions were closed, and the people were just allowed to go onto the streets."

None of this is true. First, we don't need to build more institutions. Second, the deinstitutionalization to which Trump refers — a process begun in the 1960s of systematic closing of state mental facilities and, ideally, accompanied by the creation of alternative means of support — may have created many new problems, mainly due to the lack of that second part, creating alternative supports. The pathway forward isn't to recreate the savage asylums of the past.

Third, the truth is that people talk about mental illness, especially after mass shootings, because it's politically easier to regulate the bodies of disabled people than the weapons used to kill.

For example, New York Gov. Andrew Cuomo recently proposed creating a national mental health database, something he's already done in his home state . Not only is this a violation of civil liberties, a federal registry of those Cuomo considers at risk of future crime, but there is no evidence of an easy causal linkage between gun violence and mental illness except, as journalist S.E. Smith has written , when it comes to suicide. In fact, the idea that mental illness is a principal cause of gun violence has been debunked by emergency medicine experts Dr. Megan Ranney and Dr. Jessica Gold, and Kathleen Flaherty , a Harvard-educated lawyer and survivor of involuntary commitment who is now executive director of the Connecticut Legal Rights Project.