President Trump doesn’t often ask scientists for help, but on Monday he seemed to be breaking from tradition. In a speech Monday about the deadly mass shootings in Dayton and El Paso last week, the president pitched a couple ideas for policies that might reduce the horrifying ubiquity of violent men with guns in public places. The president and other national leaders might take both literally and seriously the spontaneous chant that erupted from the crowd when Ohio governor Mike DeWine appeared at a vigil for the dead in Dayton: Do something.

This is where the science should come in. A straight-up restriction on gun ownership would work, yes, but that’s politically—constitutionally—untenable, at least as the current Supreme Court would have it. But other, more subtle options and interventions are out there. Work on reducing deaths in car crashes doesn’t demand banning all cars; requiring seat belts made a huge difference. So what’s the gun policy equivalent of a seat belt?

To answer that, you need data, hypotheses, experiments. And that’s a problem. Many basic statistics about gun violence stubbornly fail to exist. The science of how many, how often, and how bad hasn’t been done. The studies of what causes people to become violent and use firearms, of who those people are, of how to find them and stop them—they haven’t been done.

The deeper problem here is that in 1996 Congress made it illegal to put federal money toward gun control and cut the gun violence research budget at the Centers for Disease Control and Prevention. Republicans argued that such research was actually political, and designed to restrict gun ownership. (The rule is called the Dickey Amendment, and it was the result of lobbying by the National Rifle Association.) In 2018 Congress lifted the de facto ban, but didn’t fund any research. Other sources of funding exist, but research in gun violence consistently gets less money and attention than any comparable cause of death. That was mostly intentional; if you censor the explanations, then violence becomes inexplicable—senseless, or “evil.” Politicians can shake their heads and deploy thoughts and prayers instead of policy. In some ways the science of gun violence hasn’t really advanced since the Macarena was at the top of the charts.

One thing it’d be good to know: How bad is the problem? In his Monday speech, the president went on to say that since the mass murder at Columbine High School in Colorado in 1999, “one mass shooting has followed another, over and over again, decade after decade.” Yet even that simple matter of fact—whether they’ve become more frequent—is the source of debate. At least one researcher says the overall rate has been steady for decades, as the president claims; other public health researchers assert that the pace tripled in 2011, and that the first guy was overcounting by including targeted, multiple-victim homicides alongside the more randomized, mass-shooting horrors like Gilroy’s Garlic Festival or the El Paso-Juarez Walmart. The CDC doesn’t collect data on gun deaths in a way that’d make it easy to answer this question.

When the president says—as he did on Monday—“we must do a better job of identifying and acting on early warning signs,” the lack of research again dooms his ambition to failure. “We must reform our mental health laws,” the president said, and “we must make sure that those judged to pose a grave risk to public safety do not have access to firearms.” But nobody’s completely sure what those warning signs are, except in broad strokes.