Trump ended rule to block mentally ill from getting guns The action was one of his earliest as president.

 -- President Donald Trump has often pointed to mental illness as the underlying cause for mass shootings, but one of his earliest actions as president was to undo a regulation that would have made it more difficult for people with a known mental illness to buy guns.

Nearly a year ago, on Feb. 28, 2017, President Trump signed H.J. Res. 40, effectively ending the Social Security Administration's requirement to enter the names of people who receive mental health benefits into the National Instant Criminal Background Check System. This is the database used by the FBI to determine who is able to purchase firearms.

President Trump has addressed the nation about mass shootings four times throughout his time in office. On Thursday, President Trump tweeted that the shooter involved in Florida’s Parkland High School tragedy showed signs of being “mentally disturbed,” and urged for greater awareness for similar cases.

In November, President Trump cited mental health as the reason for the Sutherland Springs, Texas, church shooting that left 26 people dead.

"Mental health is your problem here. This was a very, based on preliminary reports, a very deranged individual, a lot of problems over a long period of time. We have a lot of mental health problems in our country, as do other countries. But this isn't a guns situation," President Trump said of the First Baptist Church shooting during a joint press conference with Japanese Prime Minister Shinzo Abe.

According to estimates from the previous administration, had the Obama-era regulation gone into effect, an estimated 75,000 individuals with mental illnesses would have been added to the database. These individuals would have been notified by the Social Security Administration of their possible restrictions to buy firearms but would have the opportunity go through an appeal process.

Although the rule was made effective days before Trump took office in January 2017, compliance was not required until December 2017.

At the time, the optics of the bill’s signing seemed to be downplayed by the White House despite the president’s busy, public schedule that day — he addressed the Joint Session of Congress later that evening.

The White House has not responded to ABC News' request for comment.