More than a dozen retired top military commanders, leaders and advisers, whose careers spanned both Republican and Democratic administrations, are throwing their weight behind a bill in the House and Senate that would require universal background checks for all U.S. gun sales.

In a letter Thursday, 13 former top military advisers and combat leaders urged congressional leaders in both parties to pass the bill, known in the House as HR 8, which targets private gun sales that don’t require background checks under current federal law.

“A prohibited person with dangerous intent can easily buy a gun over the internet or in a parking lot with no questions asked,” the military advisers wrote to Speaker Nancy Pelosi, House Minority Leader Kevin McCarthy, Senate Majority Leader Mitch McConnell and Senate Minority Leader Charles E. Schumer.“For those of us with extensive firearms training, who have seen the damage inflicted by a powerful weapon in the wrong hands, this is simply unfathomable,” they wrote.

The list of heavyweight signatories includes former NSA and CIA director Michael Hayden, who served under Presidents Bill Clinton, George W. Bush and Barack Obama; Stanley McChrystal, Obama’s top commander in Afghanistan; and former Coast Guard Commandant Thad Allen, who served under both Bush and Obama.

McChrystal is a member of Roll Call parent company FiscalNote’s board of directors.

The former leaders are part of a veterans coalition formed by the gun safety group founded by former Arizona Rep. Gabrielle Giffords, who left Congress in 2012, a year after surviving a shooting assassination attempt at a constituent event that left six people dead. 

The idea for the letter, according to former Army Capt. Terron Sims II, one of the letter’s signatories, is to persuade moderate Republicans, especially in the Senate, that experts on weapons use think there should be universal checks to make sure guns don’t fall into the wrong hands.

Sims highlighted a Quinnipiac University poll from February 2018 that indicated 97 percent of Americans support universal background checks.

“The data supports the legislation. The argument’s already there,” Sims said. “It’s just a matter of getting those moderate Republicans to go with the will of their constituents.”

The House Judiciary Committee approved HR 8 on a party-line 23-15 vote last week, setting up a floor vote in the near future.

Republicans have opposed the bill, saying it would have done nothing to prevent some of the recent mass shootings in which gunmen bought firearms after passing background checks.

“As written now, H.R. 8 would not have prevented any of the mass shootings in Florida in recent years,” Florida Rep. Greg Steube said in a statement last week. “The shooter in Parkland passed a background check before purchasing a firearm, the shooter at Pulse Nightclub passed a background check before purchasing a firearm, and the shooter just weeks ago that murdered five women in District 17 passed a background check before purchasing the handgun he used in the commission of that heinous crime.”

Democrats have argued that requiring background checks for private gun sales in addition to the current federal requirement for checks on licensed sales would not prevent all mass shootings, but it would be a significant step toward thwarting some.

The bill would be the most significant gun control measure passed by either the House or Senate since the ban on assault weapons expired in 2004.

“Finally, we have taken real action to combat gun violence. Finally, we have taken the procedural steps on a bill to help keep our communities safe. Finally, we will have a vote on legislation to help save lives,” California Democratic Rep. Mike Thompson said in a statement last week.

Thompson chairs the House Democrats’ Gun Violence Prevention Task Force that is steering the party’s gun violence prevention agenda.

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