The arms traffickers have left Mexico awash in AK-47s, pistols, telescope sighting devices, grenades, grenade launchers and high-powered ammunition, such as the so-called cop-killer bullets believed to be able to penetrate bulletproof vests.

"You're looking at the same firepower here on the border that our soldiers are facing in Iraq and Afghanistan," Thomas Mangan, a spokesman in Phoenix for the ATF, said in an interview.

So, we get their tired, their poor, their huddled masses yearning to breathe free, and they get our automatic weapons (and factories, but that's a different point). What happens when we start getting their tired and poor armed with what used to be our guns?

U.S. Guns Behind Cartel Killings in Mexico - washingtonpost.com