On Friday, during an interview on MSNBC's Morning Joe, Donald Trump came very close to making an extremely good point about mass shootings. Asked what he would do to prevent future mass shootings as president, Trump immediately walled off the possibility of new gun laws: "First of all, you have very strong laws on the books." But having done that, he found himself with a dilemma. He tried to blame shootings on "mental illness" — the standard line gun rights supporters use in response to gun control supporters who blame shootings on guns. But that didn't actually lead him to any proposals for something that could be done. The result was (at least by Trumpian standards) a fairly nuanced point:

you know, oftentimes this happens and the neighborhood’s just, you know, we sort of saw that about him, it really looked like he could be a problem’ but it’s often hard to put someone in an institution for the rest of their lives based on the fact that he looks like he could be a problem.

There's a real problem here. It is obviously true that many of the individuals who have committed recent mass shootings have had mental or behavioral health issues. But mental illness doesn't predict violence in the least — people with mental illness are more likely to be victims of violence than perpetrators of it.

The prospect of targeting and stigmatizing people with mental health issues as a group, in reaction to mass shootings, is morally abhorrent. But Jesse Singal, of the Science of Us blog at New York magazine, has written an extremely good piece making a good-faith effort at working through it empirically. He sets out to figure out whether there are any mental or behavioral factors that predict who's disposed to commit mass shootings, as a way to figure out whether there's any effective policy response that focuses on controlling people rather than guns.

The answer, he finds, is no. Here's the key point from Columbia psychiatrist Dr. Paul Appelbaum, which sounds, in a weird way, like Trump's point on Morning Joe:

any attempt to predict who is most likely to commit a mass shooting — and therefore prevent it — runs up against the fact that these events are extremely rare, and as a result have only the broadest, least useful risk factors associated with them. [...] The risk factors that are linked to these events — basically, being an angry young man — are so widespread in the population, he explained, and so weakly predictive of an individual actually committing a mass shooting as to be practically useless. "The answer is yes, at least of the most highly publicized, most fear-inducing cases of stranger shootings, by and large they are angry young men," said Appelbaum. "But that doesn’t get you very far, because there are a lot of angry young men who are angry for all kinds of reasons, and unless one wants to lock them all up or put them all under 24-hour surveillance, it’s really impossible to build on a description that general to come up with effective preventative approaches."

As a result, says Appelbaum, he's not talking about the "causes of violence" as a psychiatrist anymore. As Singal writes:

Instead, he’d prepared a one-size-fits-all statement for the media that concluded, "If you tell me that there’s nothing we can do about guns, I’d say then we’re done. We’ve conceded that we are willing to tolerate periodic slaughters of the innocent. There’s nothing more to say.’"

In other words, just because there's no answer to "how can we predict who will commit mass shootings?" doesn't mean there's no answer to "how can we prevent mass shootings?" To Appelbaum, there is a clear answer to the second — gun control — so it doesn't matter, from a policy perspective, whether there is an answer to the first.

But Trump, whose base is ferociously opposed to gun control, doesn't have that option. As a result, he's left with the terrible dilemma: monstrously overbroad mass institutionalization, or inaction. And while he started the Morning Joe interview reasonably conflicted between the two, when the interviewer asked him, "So is your opinion that some people are going to slip through the cracks?" Trump embraced that option enthusiastically:

You know, it’s not politically correct to say that, but you’re going to have difficulty, and that would be for the next million years you’re going to have difficulty. People are going to slip through the cracks and even if you did great mental health programs, people are going to slip through the cracks! [...] you are going to have difficulties. You’re going to have difficulties with many different things, not just this. And that’s the way the world works. And by the way, that’s the way the world always has worked.

That sounds less like an actual answer than like that Onion headline: "'No Way to Prevent This,' Says Only Nation Where This Regularly Happens." But it's very revealing. If your only option is to try to regulate people and predict what they will do, Trump is right: There really is no way to prevent mass shootings. Where one might disagree with him is whether more strictly regulating people is really easier or more acceptable than more strictly regulating guns.