The hypocrisy grows all too gruesome: The Justice Department pronounced the Mexican drug cartels “a national security threat” this week, even as American gun dealers along the border were busily arming the cartels’ murderous gangs. Mexico complains that American dealers supplied most of the 20,000 weapons seized last year in drug wars in which 6,000 Mexicans died.

A vast arms bazaar is rampant along the four border states, enabled by porous to nonexistent American gun laws. Straw buyers can pick up three or four high-powered war rifles from one of more than 6,600 border dealers and hand them off to smugglers. They easily return to Mexico, where gun laws are far less permissive.

Licensed dealers routinely recruit buyers with clean criminal records to foil weak laws and feed the deadly pipeline, according to a report by James C. McKinley Jr. in The Times. The countless unlicensed “gun enthusiasts” free to deal battlefield rifles at weekend shows, thanks to loophole-ridden laws, are a second source.

The federal government is allowed to only trace weapons used in crimes and has no idea of the full scope of the border trade, which accounts for 9 out of 10 recovered weapons.