In the aftermath of another mass shooting in America, there’s new attention to a law that Congress passed earlier this year — effectively making it easier for people with mental illness to buy a gun.

In February, President Donald Trump and Congress enacted a law that blocked a last-minute regulation from former President Barack Obama’s administration that required the Social Security Administration to disclose to the FBI information about people who are getting disability benefits due to severe mental illness. The rule was meant to make it a bit easier for the FBI to flag those with severe mental illness while doing a background check on a firearm purchase.

But the National Rifle Association (NRA) and American Civil Liberties Union (ACLU), backed predominantly by Republicans in the House and Senate, argued that the rule violated the Second Amendment rights of people with mental illness without adequate due process.

So Congress voted to repeal the rule. And with the Congressional Review Act, the House and Senate only needed a simple majority, along with the president’s approval, to undo the recently enacted regulation.

The Obama-era gun regulation wouldn’t have had a massive impact on gun violence in the US, since it’s estimated that it would only affect about 75,000 people. And there are serious arguments against the Obama-era rule, which is why this is a rare situation in which typically liberal and typically conservative groups worked together on its repeal.

But anything that makes it easier to obtain a gun, the research suggests, will likely worsen gun violence. After all, America already has some of the weakest gun laws in the developed world — and repealing a rule that made it a little tougher for some people to buy a gun likely makes that worse.

The rule tasked the Social Security Administration with turning over information to the FBI

The Obama rule, which was finalized in December, didn’t target just anyone who got disability benefits for a mental illness. It specifically concerned people with mental illnesses so severe that they can’t handle their own disability benefits — under the rationale that someone who can’t handle his own disability benefits is probably too ill to handle a gun.

The criticism, voiced by the NRA, ACLU, and congressional defenders of gun rights, is that the rule robbed people of their Second Amendment rights without due process.

Typically, gun laws restricting access to firearms for those with mental illnesses dictate who is too ill to own a gun through a formal review by a court or other legal authority.

But the Obama rule didn’t work through the courts. Instead, once a person was deemed unable to handle disability benefits on his own (which does require a hearing), his information was sent to the FBI, and he would from then on be unable to pass a background check.

The rule would have allowed people to appeal the determination in court or to the Social Security Administration, but only after their information was already sent to the FBI.

Ari Freilich, a staff attorney at the Law Center to Prevent Gun Violence, argued that all of these checks, from the hearing to appeal, are adequate due process. “It’s fair to say that due process could be improved through making the bureaucracy more efficient and ensuring that these folks have more adequate notice,” he said. “But before they can be reported to the FBI background check system, they do have to receive notice, they do have to have the opportunity for a hearing.”

By itself, the rule probably wouldn’t have a huge impact on gun violence, since it only affected 75,000 people. But supporters argued it could prevent some acts carried out by people with serious mental illnesses, pointing to previous mass shootings in which the perpetrator showed signs of mental illness. (So far, there’s no evidence the shooter in Las Vegas had any history of mental illness.)

“These are not people just having a bad day,” Rep. Mike Thompson, a California Democrat, argued. “These are not people simply suffering from depression or anxiety or agoraphobia. These are people with a severe mental illness who can’t hold any kind of job or make any decisions about their affairs, so the law says very clearly they shouldn’t have a firearm.”

The NRA and ACLU said the rule violates the rights of people with mental illness

The NRA, ACLU, and legislators disagreed that the rule has enough checks in place — arguing that without the traditional court process, the Obama rule effectively takes away a person’s constitutional rights without due process.

“The Social Security Administration not only overstepped its mission with this regulation, it discriminated against certain Americans with disabilities who receive Social Security benefits,” Rep. Kevin Brady, a Texas Republican who chairs the Ways and Means Committee, said. “The agency should be focused on serving all of its beneficiaries, not picking and choosing whose Second Amendment rights to deny.”

The rule also perpetuates, critics said, the stigma that people with mental illness are behind gun violence in America. In reality, studies show people with mental illness are more likely to be victims, not perpetrators, of violence, and that very few violent acts — about 3 to 5 percent — are carried out by those with serious mental illness.

Jonathan Metzl, a Vanderbilt University professor who studies the intersection of guns and mental illness, generally agrees, based on the evidence, that tighter restrictions on guns save lives. But, he told me, gun restrictions that target mental illness “reinforce stereotypes that people with mental illness are ticking time bombs.” Metzl added that he’d rather focus on factors that are much more likely to contribute to gun violence, including general access to firearms for everyone, a history of violence, and drug and alcohol abuse.

That doesn’t mean that people with mental illness can’t present a danger to themselves or others. In some (but not all) high-profile shootings mental illness appeared to play a role. And the risk of suicide is much higher, according to the empirical evidence, if a gun is easily accessible.

“There’s overwhelming evidence that the mentally ill kill themselves more frequently if they have access to guns,” John Donohue, a Stanford University researcher who studies gun policy, told me. “So you’re reducing suicides.”

But even some advocates of stricter gun laws don’t like the idea of revoking someone’s rights without due process in court just because he’s mentally ill — and, like it or not, gun rights are shielded by the Supreme Court’s current interpretation of the Second Amendment. That’s why the ACLU opposed the rule, arguing a disability shouldn’t allow the automatic denial of any constitutional right.

The research is clear: More access to guns means more gun deaths

Still, Metzl worried that the rule’s repeal was “a first step” in “a broader attack” on gun laws, pointing out that laxer gun laws are something that Trump and Republicans supported on the 2016 campaign trail. “If this was the only action that Congress was going to take on guns, I actually would be kind of comfortable with it,” he said. “At the same time, I don’t think this act can be seen outside of the context of a broader attack on sensible gun legislation and regulation more broadly.”

The repeal of the Obama rule or any gun restrictions would diminish America’s already weak gun laws. And, based on the research, those weak gun laws already lead to more gun deaths.

No other developed country in the world has anywhere near the same rate of gun violence as America. The US has nearly six times the gun homicide rate of Canada, more than seven times Sweden’s, and nearly 16 times Germany’s, according to United Nations data compiled by the Guardian. (These gun deaths are a big reason America has a much higher overall homicide rate, which includes non-gun deaths, than other developed nations.)

What’s more, there appears to be a correlation between America’s high levels of gun violence and gun ownership, as this other chart from researcher Josh Tewksbury shows:

Research reviews by the Harvard School of Public Health’s Injury Control Research Center have concluded that more gun ownership leads to more gun violence. Other factors, such as socioeconomic issues, contribute to violence, but guns are the one issue that makes America unique relative to other developed countries in comparable socioeconomic circumstances.

Studies have found this at both the state and country level. Take, for instance, this chart, from a 2007 study by Harvard researchers, showing the correlation between statewide firearm homicide victimization rates and household gun ownership after controlling for robbery rates:

A more recent study from 2013, led by a Boston University School of Public Health researcher, reached similar conclusions: After controlling for multiple variables, the study found that a 1 percent increase in gun ownership correlated with a roughly 0.9 percent rise in the firearm homicide rate at the state level.

This holds up around the world. As Zack Beauchamp explained for Vox, a breakthrough analysis in 1999 by UC Berkeley researchers Franklin Zimring and Gordon Hawkins found that the US does not, contrary to the old conventional wisdom, have more crime in general than other Western industrial nations. Instead, the US appears to have more lethal crime — and that’s driven in large part by the prevalence of guns.

“A series of specific comparisons of the death rates from property crime and assault in New York City and London show how enormous differences in death risk can be explained even while general patterns are similar,” Zimring and Hawkins wrote. “A preference for crimes of personal force and the willingness and ability to use guns in robbery make similar levels of property crime 54 times as deadly in New York City as in London.”

These studies aren’t the only ones to reach such conclusions. Multiple reviews of the research, including the Harvard Injury Control Research Center’s aggregation of the evidence, have consistently found a link between gun ownership and gun deaths after controlling for other factors.

Guns are not the only factor that contributes to violence. (Other factors include, for example, poverty, urbanization, and alcohol consumption.) But when researchers control for other confounding variables, they have found time and time again that America’s high levels of gun ownership are a major reason the US is so much worse in terms of gun violence than its developed peers.

That helps explain why the most rigorous reviews of gun policies have concluded that stricter gun laws can reduce gun violence and deaths. A 2016 review of 130 studies in 10 countries, published in Epidemiologic Reviews, found that new legal restrictions on owning and purchasing guns tended to be followed by a drop in gun violence — a strong indicator that restricting access to guns can save lives.

America, however, is unique in the developed world in that it constitutionally enshrines the right to own a gun — and that brings special legal protections for those rights.

But the research suggests that those extra rights come at a cost of more gun deaths. That’s why many public health researchers would like to see a focus on restricting guns in general, not just for those who are mentally ill.

“If you really want to stop gun injury and death in the United States, we could also think about ways to better regulate guns to sane people,” Metzl said. “They specifically are responsible for much more of the gun injury and death in this country.”