Today’s Washington Post reports an often heard but highly inaccurate statement: 90% of guns employed in the drug cartel killing spree come from the U.S.  It is a factoid prominently stuck in the minds of leaders and the media, some of whom use this misrepresentation in support of reimposing extensive federal gun restrictions.

The Post reports that Mexican law enforcement seized 35,000 weapons between December 2006 and the present. Of that total, the Post reports that 13,149 weapons were then reported to the U.S. by our southern neighbor. That leaves 21,851 guns for which Mexican authorities have not submitted information to the U.S., probably because it is apparent that those 21,851 guns were not manufactured in the U.S.

Other sources of weapons include surrendered or stolen weapons from Mexican military stocks, arms smuggled in from Central America, international black market purchases, illegally stolen items in the U.S., etc. Little attention is given to these sources by those pressing for new federal gun restrictions.

Before Congress recently, ATF Special Agent William Newell reported that in FY 2008, the Mexican government sent requests for traces for 7,743 guns and reported that for the same period 3,567 were traced back to suppliers in the U.S. He omits to say how many guns were seized by the Mexicans at that time, but this is far from the 90% of guns used in drug violence coming from the U.S. that is thrown about. A recent analysis by Fox News puts the confirmed traces at 17% of the total of guns seized in Mexico.

At best, the methodology used to get to that statement that 90% of the guns used in drug violence in Mexico come from the U.S. requires careful scrutiny is highly misleading.

And, as observed, George W. Grayson, a Mexico scholar at the College of William and Mary and author of the monograph “Mexico’s Struggle With ‘Drugs and Thugs,’ it’s convenient for the cartels to be able to shop in Arizona, New Mexico, Texas and elsewhere, but stopping the U.S. trade, would merely place a thorn in the side of the cartels, rather than an AK-47 in the heart.”

The Mexican government will nonetheless likely press President Obama to act boldly with measures along the lines advocated by Ambassador Arturo Sarukhan during a Face the Nation interview this past Sunday.

The Mexican Ambassador argued that the old federal ban on so-called “assault weapons” expired in 2004, and “since then we have seen a rise of assault weapons being seized in Mexico. There is a direct correlation between the expiration of the assault weapons ban and our seizures of assault weapons.” [But note the figures available do not indicate how many of the guns traced to the U.S. even fall under the overbroad definition of “assault weapons” in the now-expired federal ban.]

Sarukhan admitted the Mexican government cannot determine how Congress and the Obama administration would move on the ban, but he claimed that reinstating the ban “is one of the instruments … that could have a profound impact on the number and the caliber of weapons doing down to Mexico.”

Advocating specific legislation to foreign government, i.e. the U.S., is a role Ambassadors in Washington generally reserved for off the record conversations with host officials. U.S. Ambassadors in Mexico City have never been popular when issuing legislative guidance to Mexican congress.

The Mexican offensive against U.S. guns appears to be a part of the shifting rationale to explain the logic behind the drug fight, comments former Mexican foreign minister Jorge Castañeda in a disturbingly provocative Slate piece without a clear rationale and, perhaps, without adequate strategic preparations.

Calderon defended his move against the Drug Cartels, in the following ways, according to Castañeda’s analysis, “first, the cancer of the drug trade was eating away at the civic fabric of Mexico’s democracy and its institutions. Then it became a matter of saving our children, because Mexico’s consumption rates were rising (a claim the government has yet to back up with persuasive evidence). While in London for the G20 summit, President Calderón gave the impression that his decision to unleash the military on the cartels was made necessary by the United States lifting the 1994-2004 ban on assault rifle sales.”

One of the goals of the Mexican government while President Obama in Mexico City today and tomorrow is to pressure him to do something about gun regulations. He will need to push back. The topic of “assault weapons” is just one piece of the very troubling drug violence dynamic. It should not be become a dividing point or litmus test between our two nations.

Angering millions of Americans concerned about Second Amendment freedoms and worried about their ability to defend themselves in the event of a possible “spillover” of Mexico’s drug violence across the border will surely do more harm than good.