DO AMERICA’S failed gun policies contribute to the terrible violence in Mexico? Alejandro A. Poire Romero makes a compelling case that the answer is yes.

Law enforcement officials in both countries acknowledge that 70 to 80 percent of the traceable guns seized in Mexico can be tracked to the United States. Mr. Poire Romero, a top Mexican national security and criminal justice official, offers additional evidence that the United States has been an enabler of the violence.

In 2005 roughly one-third of the seized guns were assault weapons. Today, according to Mr. Poire Romero, assault weapons represent 60 to 65 percent of the guns confiscated by Mexican authorities. The assault-weapons ban in the United States lapsed in 2004.

“The significant rise in violence and the increase in the number of public officials killed in Mexico coincides with lifting of the assault weapons ban,” Mr. Poire Romero said.

Mr. Poire Romero met with Post editors and reporters on the day that Attorney General Eric H. Holder Jr. was again being grilled on Capitol Hill about “Operation Fast and Furious,” during which U.S. law enforcement agents, in order to trace weapons to higher-ups in a criminal enterprise, failed to interdict guns bought by suspected straw purchasers. The operation, a version of which was undertaken during the George W. Bush administration, was deeply flawed; some 2,000 weapons are unaccounted for. Weapons traced to Fast and Furious purchases were found on the scene of the 2010 killing of a Border Patrol agent. These revelations led to the resignation of the U.S. attorney in Phoenix and reassignment of the acting director of the Bureau of Alcohol, Tobacco, Firearms and Explosives.

Mr. Poire Romero calls Fast and Furious “an issue of concern” for Mexico. “It’s clear that we did not know and would never have approved of an operation that let guns walk into Mexico,” he said, noting that the Mexican government — in addition to the U.S. Congress and the Justice Department’s Office of Inspector General — is conducting its own investigation.

Yet Fast and Furious was a well-intentioned, misguided response to — and not the cause of — the proliferation of illegal guns in Mexico. To stanch that flow, the Obama administration and Congress should heed the pleas of Mr. Poire Romero and his countrymen by reviving the assault weapons ban and closing the gun show loophole that makes it far too easy to sell weapons without a background check. The White House and lawmakers should work to enact a federal firearms trafficking statute and call for stiffer penalties for illegal straw purchases. Lawmakers also should confirm a chief for the ATF and give the beleaguered agency enough money and personnel to fulfill its mission of keeping illegal guns out of the hands of criminals on both sides of the border.