President Donald Trump has frequently blamed "the mental illness problem" for mass shootings, but made it easier for people with certain mental illnesses to buy guns.

Trump signed a bill blocking the enactment of an Obama-era rule that would have entered Americans who receive Social Security/Disability benefits for mental illnesses into the National Instant Criminal Background Check System to prevent them from buying guns.

into the National Instant Criminal Background Check System to prevent them from buying guns. But the American Civil Liberties Union, which rarely sides with the Trump administration, supported the GOP and Trump in repealing the rule.

The ACLU argued that greater surveillance on people with mental illnesses was a dangerous slippery slope that could lead to greater infringements on the civil liberties of people with mental illness.

The assumption that mass shooters are mentally ill or that mentally ill people are at a higher risk to commit violence is largely unfounded.

Visit Business Insider's homepage for more stories.

President Donald Trump has frequently blamed "the mental illness problem" for mass shootings and even suggested "involuntary confinement" for mental illnesses, but made it easier for people with certain mental illnesses to buy guns.

After previous mass shootings and the most recent two shootings in El Paso, Texas and Dayton, Ohio that killed 31 people and injured dozens of others over the weekend, Trump and fellow Republicans have jumped to blame mental illness as the culprit.

"We must reform our mental health laws to better identify mentally disturbed individuals who may commit acts of violence and make sure those people, not only get treatment, but when necessary, involuntary confinement," Trump said in Monday remarks at the White House, adding, "mental illness and hatred pulls the trigger, not the gun."

Not only have researchers found no causal relationship between mental illness and mass shootings, but Trump himself blocked the enactment of a proposed Obama-era rule that made it more difficult for some individuals with diagnosed mental illnesses to obtain firearms.

Read more: Trump said people with mental illness should be 'involuntarily confined' if necessary to prevent mass shootings, despite research showing a lack of connection between mental illness and gun violence

In the wake of multiple mass shootings, the Obama administration proposed a new rule — which never went into effect — to enter Americans who receive Social Security/Disability benefits for mental illnesses and whose benefits are managed by a family member or guardian into the National Instant Criminal Background Check System, preventing them from being able to buy guns.

Shortly after Trump took office in January 2017, Congress passed a resolution scrapping the proposed rule, which Trump signed. According to NBC, the Obama administration had estimated that up to 75,000 people would have been affected by the rule.

Trump seems to have undermined his own stated mission to stop guns from getting into the hands of some people with mental illnesses. But in an unexpected twist, the American Civil Liberties Union, which rarely sides with the Trump administration and has sued them dozens of times, supported the GOP and Trump in repealing the rule.

In a February 2017 memo, ACLU legislative counsel Vania Leveille and disability counsel Susan Mizner wrote that the rule wrongly tried to impose a one-size-fits-all solution by lumping a diverse group of people with a wide range of mental illnesses into the same category, denying them due process.

They noted that the subset of people receiving disability benefits managed by another person range all the way from "young people with depression and financial inexperience to older adults with Down syndrome needing help with a limited budget."

"Gun control laws, like any law, should be fair, effective and not based on prejudice or stereotype. This rule met none of those criteria," they argued, adding that "no data — none — show that these individuals have a propensity for violence in general or gun violence in particular."

Read more: The men behind the US's deadliest mass shootings have domestic violence — not mental illness — in common

The existing research on the link between mental health and gun violence has found that the assumption that mass shooters are mentally ill or that mentally ill people are at a higher risk to commit violence is largely unfounded.

On Monday, the American Psychiatric Association said in a statement that the "overwhelming majority of people with mental illness are not violent and far more likely to be victims of violent crime than perpetrators of violence."

A 2015 research study from Jonathan Meltz and Kenneth MacLeish of Vanderbilt University found that "less than 3% to 5% of US crimes involve people with mental illness, and the percentages of crimes that involve guns are lower than the national average for persons not diagnosed with mental illness."

James Knoll and George D. Annas further wrote in the 2016 book "Gun Violence and Mental Illness" that "mass shootings by people with serious mental illness represent less than 1% of all yearly gun-related homicides."

Knoll and Annas said that because people with diagnosed mental illnesses account for a such a small percentage of shootings, laws and regulations specifically targeting people with mental illnesses "will be the extremely low yield, ineffective, and wasteful of scarce resources."

The ACLU argued that greater surveillance on people with mental illnesses was a dangerous slippery slope that could lead to greater infringements on the civil liberties of people with mental illness.

"Adding more innocent Americans to the National Instant Criminal Background database because of a mental disability is a disturbing trend — one that could be applied to voting, parenting or other rights dearer than gun ownership," Leveille and Mizner wrote.

Read more:

After mass shootings, people may feel more willing to shoot someone, research says

The Trump administration has actually cut government resources to fight white supremacy and domestic terrorism

Trump said mental illness 'pulls the trigger, not the gun,' but a wealth of research shows that's bogus