The cry that rose from the crowd at Sunday’s vigil in Dayton should resound throughout this blood-spattered nation.

“Do something! Do something! Do something!”

The words rose from the same streets where six Dayton cops had shown such remarkable courage in the early morning hours.

Sgt. William C. Knight, Officer Brian Rolfes, Officer Jeremy Campbell, Officer Vincent Carter, Officer Ryan Nabel, and Officer David Denlinger deserve more than just our admiration.

We owe it to them to reduce the chances that they and cops elsewhere will have to place themselves in such peril in the future.

Expanded background checks would generally help but would not likely have prevented either of the most recent mass shooters from acquiring their weapons.

And, in many states, there remains fierce opposition to banning assault rifles and high-capacity magazines such as allowed the Dayton gunman to kill nine people in 30 seconds. He no doubt would have killed many more save for the Dayton cops who might be called the Magnificent Six.

But gun-rights champions and gun-control advocates agree on one thing: Mental illness is a factor in mass shootings, with studies showing that about one-third of such shooters have severe untreated mental issues.

President Trump appeared to use the issue as a way to duck even talking about meaningful gun control when he declared on Monday, “Mental illness and hatred pulls the trigger, not the gun.”

Well, Mr. President, whether or not it was just a dodge, you did call for “bipartisan solutions” regarding mental illness and gun violence.

Here is one proposal put forward by a prominent California psychologist that could actually make a difference, and draw support from Republicans and Democrats.

Two years and too many mass shootings ago, Dr. John Caccavale, 70-year-old executive director of the National Alliance of Professional Psychology Providers, issued a paper titled “Gun Ownership and Mental Health.”

Caccavale asserts in a subsection titled “A Proposal To Integrate Mental Health Assessment Into Access To Guns” that his plan is “consistent with protecting the constitutional right to acquire firearms while reducing gun violence by people who may be impaired and should be denied access to guns.” The core of it is outlined in a subsection titled “Assessment Clearance.”

“ A person who is experiencing a psychotic disorder, major mood disorder, cognitive deficit or severe personality disorder is most probably impaired and should not be allowed to have access to a firearm. ”

“Any person who seeks to purchase a gun of any type of firearm that is legal under a statute will be required to obtain a standardized psychological assessment from a licensed doctoral level mental health specialist,” the proposal states. “The sole objective of the assessment is to identify factors that may be particularly related to an impairment that can be related to harm to oneself or others.”

In short, every prospective gun owner gets screened.

The proposal goes on, “For example, a person who is experiencing a psychotic disorder, major mood disorder, cognitive deficit or severe personality disorder is most probably impaired and should not be allowed to have access to a firearm while experiencing any of the above. This is not a finite list.”

The proposal adds, “Persons who are denied clearance can appeal a denial. Persons who can demonstrate that they no longer are impaired can seek another assessment.”

But, the proposal says, “No person shall be allowed to purchase a firearm or related products without having this certificate of clearance.”

Lest the Second Amendment crowd howl, the proposal observes, “The issue then becomes putting our focus on the people who use guns to kill people, which is consistent with some who chant that ‘Guns don't kill people. People kill people.’”

In 2016, Caccavale tested the possible bipartisan appeal of his proposal by sending it to nine Republican members of congress whose legislative portfolios include mental health: Rep. John Katko, Rep. Darrell Issa, Rep. Marcy Kaptur, Rep. Joe Wilson, Rep. Mark Mullin, Rep. Timothy Murphy, Rep. Tom McArthur, Rep. Kay Granger and Rep. Elise Stefnik. He received no response.

“Nothing,” he told The Daily Beast on Monday. “Not even one of the canned responses.”

He fared no better with the California state legislature.

“What happens is they really don’t want to do anything,” he said.

In March, Caccavale—Brooklyn-reared, but Southern California-educated and -based—met the congressman for the district where he has long practiced, Rep. Alan Lowenthal. Caccavale expected better luck, as Lowenthal is himself a psychologist as well as a Democrat.

“He says, ‘I’ll take a good look at this. This looks like it has a lot of merit,’” Caccavale remembers.

Caccavale also recalls, “He said, ‘I see you have great passion on this, John.’ I said, ‘Passion? It’s not a passion issue. People are being murdered.’”

Lowenthal seems to have done nothing. His spokesman did not respond to a request for comment from The Daily Beast.

People kept getting murdered. And mental health continued to be a major factor as one mass shooting followed another, two in 13 hours over this past weekend,

“Every time there’s another shooting, my heart just goes,” Caccavale said Monday.

Cacavalle is all the more frustrated because his plan is so simple.

“We’re not talking about Big Brother,” he said.

The testing would be little different than is currently used to screen prospective cops and firefighters as well as a variety of employees in the public and private sectors.

“It’s not a very big deal,” he said. “It won’t even cost anything, except for the ones who want to get guns.”

Caccavale offered a psychological assessment of politicians in general.

“They’re lazy as hell,” he said.

He has a particular diagnosis for politicians who say mental health is a major factor but do nothing about it as the carnage continues.

“It's their mental health. That’s the problem,” he said.

The proposal is here (PDF) for anyone who wants to study its details.

He notes it is not itself a solution to gun violence, just one easy way to reduce it.

Meanwhile, remember the Magnificent Six the next time you hear someone trash cops in general. And keep up the cry at the vigil where they faced a disturbed young man in body armor wielding a weapon of war that could kill nine in less than 30 seconds.

Do something!