PHOENIX -- X-Caliber, a gun store in a nondescript neighborhood in this city's northern section, has become embroiled in Mexico's turmoil. The chaos there is the result of the Mexican government's decision to wage war against rampant drug cartels that are fighting mostly against each other but also against the portions of Mexican law enforcement they have not corrupted. Operating in that nation's north, they are serving this nation's appetite for illegal narcotics and illegal immigrants.

The gun shop's proprietor, the name of whose shop might indicate familiarity with Arthurian legend, is on trial here, accused of selling at least 650 weapons, including AK-47 rifles, in small lots to "straw buyers" -- persons who illegally pass the weapons on to the cartels, thereby fueling the violence that killed more than 6,000 Mexicans last year. That was more than 2,000 above the 2007 toll and fewer than will die if the rate of killing so far this year continues. (U.S. military fatalities in Iraq in six years number 4,249.) Fortunately, most of the fatalities are members of the warring cartels.

The prosecution of the proprietor is part of the U.S. attempt to stop the southward flow of weapons and bulk currency while Mexico combats the northward flow of drugs, and of human beings brought by "coyotes." But although almost all the cartels' weapons come from the United States, the cartels are generating upward of $15 billion annually from drugs, human trafficking and extortion. So they will find ways to get guns -- and grenades and other military weapons -- for their internecine disputes about control over routes for smuggling drugs and people.

When Gen. Michael Hayden stepped down as CIA director, he listed Mexico among America's biggest national security concerns. But even allowing for the stresses arising from the global economic downturn, speculation that Mexico, with the world's 13th-largest economy, is sinking toward the status of a "failed state" is far-fetched, as is the idea that the cartels can withstand a determined drive by the Mexican military, assisted by U.S. military technologies.

The turmoil is, however, taking a toll on Arizona, which has a 370-mile border with Mexico. Terry Goddard, Arizona's attorney general, says this is a "transit state" not a "destination state." Phoenix is a distribution center for smuggled drugs destined for more than 230 American cities, and for people. Each commodity is stashed in different "drop houses." The people are kept in what Goddard calls "cattle-car conditions." He says that although a million people a year are moving north through Arizona, it is still a seller's market for traffickers in human beings.

Extrapolating from wire transfers of hundreds of millions of dollars from customers in dozens of U.S. states to smugglers operating in Arizona, Goddard believes that the "coyotes" who bring in the human contraband are extremely violent extensions of the cartels. One gang will swoop down on a "drop house" holding smuggled persons, or on a truck carrying such persons on the interstate from Tucson, and then "negotiate" their own deals with people who thought they had already paid for the smuggling. Some who object are shot in the head, which is, Goddard says, "a pretty good technique" for encouraging payments from the others. He estimates that half of Phoenix's 169 murders last year were related to human and drug smuggling.

Mexico, he says, is no longer importing up to four times more pseudoephedrine than its pharmaceutical industry requires. This ingredient was used to make methamphetamines destined for the U.S. market. Today, measured by volume (millions of pounds) and profit (up to 70 percent of the cartels' earnings), the biggest business is still marijuana. It is shipped in two-ton lots, in trucks that cross over the border fence without touching it, using "bridges" that can be assembled in 90 seconds at places identified by spotters who are equipped to live in the desert for weeks at a time. They can report where U.S. border patrols are at any moment.

All this has rekindled the debate -- a hardy perennial -- about crimping the cartels' marijuana market by legalizing their product in the United States. Whatever the merits of legalization -- and there are certain to be costs -- it will not happen in the foreseeable future, which is where Arizonans must live.

There are more than 6,600 licensed American gun dealers on the 2,000-mile border with Mexico. They should obey the law, even though most of the victims of the cartels' violence deserve to be.