It took an hours-long shootout for the Mexican army to kill drug kingpin El Mencho in February. Mexico coordinated with US intelligence during the operation, but Donald Trump wasn’t ready to forgive the country that he has repeatedly accused of flooding the United States with drugs. “Mexico must step up their effort on Cartels and Drugs!” he wrote shortly afterward. In decrying Mexican “narcoterrorism,” Trump doesn’t mention that the violence goes both ways, with AR-15s flowing south while fentanyl flows north; indeed, 80% of the guns that El Mencho’s men used to hold off the military traced back to the United States.

Mexico has only two legal gun stores. To buy a weapon from them, Mexicans have to submit dozens of documents and wait several months for approval. Mexico nevertheless had the world’s highest number of gun homicide victims in 2023, and its cartels are armed to the teeth. In 2011, the government raided a Zetas weapons cache that contained 154 rifles and shotguns, over 92,000 rounds of ammunition, four mortar shells, and two rocket-propelled grenades. The mortars and RPGs are usually stolen from police and the military, but the rifles and shotguns might have come from a gun store near you. As many as 500,000 firearms are smuggled across the southern border annually; American citizens often buy them legally from licensed gun stores and dealers in Texas, Arizona, and other southwestern states with lenient gun laws. After the handoff, the gun makes a quick trip over the border, whose security systems are primarily designed to catch drugs coming into the United States, not weapons heading out. Some smugglers report simply walking into Mexico with entire firearms taped to their bodies.

The multibillion-dollar effort to stop drug trafficking has not included a substantial crackdown on “straw purchases,” the purchase of a firearm by a proxy buyer on behalf of someone else, perhaps because it would require the United States to institute real background checks for gun buyers. A federal task force established in 2020 to prevent arms trafficking has only seized 4,300 Mexican-bound guns, leaving millions more to cross the border unscathed. Six years ago, the Mexican government lodged a protest against US inaction by suing several leading American gun manufacturers. Because 70% to 90% of guns recovered at Mexican crime scenes came from the United States, the country’s lawyers argued that their American gunmakers ought to be held liable. The US Supreme Court unanimously threw out the lawsuit in mid-2025, a few months after Trump officially designated Mexican cartels as foreign terrorist organizations. Ironically, Trump’s offensive has been a bonanza for arms traffickers, who have ramped up shipments in order to meet demand from cartels preparing for a battle with the United States and Mexico. For smugglers, the main focus “at the moment is guns, not the drugs, because of the war,” one Sinaloa cartel operative told the New York Times.