Drug smugglers have already beaten Trump's wall.

• Author: Brown, Theresa Cardinal

DURING A SPEECH announcing his intention to seek the presidency, Donald Trump stumbled on what would become a signature issue for his campaign: Mexico. "When Mexico sends its people, they're not sending their best," he said. "They're sending people that have lots of problems, and they're bringing those problems with them. They're bringing drugs. They're bringing crime."

The "great, great wall" Trump wants to build isn't just aimed at stopping the people from crossing illegally into the United States; it's also supposed to stop the narcotics. But it isn't going to work.

To be blunt, the U.S. government is not likely to outspend the drug cartels at the border. Even if Trump is willing to put up the $21.6 billion the Department of Homeland Security estimates constructing a barrier would cost, the illegal drug trade is a $350 billion international business, according to the United Nations World Drug Program. A 2014 report from RAND Corp. estimated the American drug market for the four most prevalent illicit drugs--cannabis, heroin, cocaine, and methamphetamines--at $100 billion annually. The profit incentives to find ways over, under, around, orthrough any border infrastructure are high, and the cartels have more than enough money to spend on R&D.

Drug smugglers are already using a wide range of techniques to move merchandise across the border, and doing so quite successfully. On the low-tech end of the spectrum are so-called drug mules. Immigrants wishing to cross the border and their coyotes, or paid guides, must first pay tribute to the cartel that controls the plaza, or approach to the border. The payment may be in cash, but it often also includes an agreement by the migrants to carry drug loads withthemas they cross. This is actually a pretty high-risk import strategy: If the mules are caught, the cartels lose the drugs. But more often than not, the smugglers are using migrants as a decoy to draw the attention of the Border Patrol while they move larger loads across elsewhere.

Current border infrastructure, such as steel mesh fencing, is easy enough to cut through with a Sawzall, and such half-moon gashes are everywhere, especially in places such as San Diego. A 2009 Government Accountability Office report said Congress would have to spend $6.5 billion over 20 years just to repair the existing fencing.

Another low-tech method to foil existing infrastructure involves using catapults to launch bales of drugs over the fence. One such device...