Guns purchased legally in the U.S. don’t end up only in the hands of American criminals; they may also be finding their way into the possession of Mexican drug trafficking organizations. Guns bought mostly in the Southwest United States account for roughly 70 percent of the weapons seized in Mexico from 2009 through 2014, a report from the U.S. Government Accountability Office says.

The report comes as the United States grapples with a national debate over gun control while mass shootings take place on an almost regular basis. President Barack Obama and the Democrats looking to replace him in 2017 have called for comprehensive firearm controls to be passed in Congress, but Republicans have firmly pushed back on the grounds that doing so would violate Second Amendment rights.

The GAO report relied on data analyzed year by year in which the Justice Department’s Bureau of Alcohol, Tobacco and Firearms traced weapons confiscated in Mexico back to their origins. Most of the guns were purchased legally at gun shows or gun shops in the U.S. before being brought south. The smugglers have also been complicating the tracing ability for investigators, who said the weapons are often being broken down into parts before being smuggled into Mexico.

Obama has repeatedly addressed the issue of gun control as president, though it was not until last week that he exercised his executive authority to expand background check requirements. Even with that action, and the recent avowal from U.S. Attorney General Loretta Lynch to ensure that those executive actions last beyond his presidency, many have said that his actions aren’t enough in the long run.

 A recent poll shows that the majority of Americans support stricter measures.