President Donald Trump has made it clear that he believes drug trafficking is primarily a border control issue, and that solving the drug crisis is as simple as constructing a massive wall along the Southern border.

But during a joint press conference on Thursday, Colombian President Juan Manuel Santos declined to endorse that strategy, telling reporters that the drug crisis is a complex, international issue that requires "collaboration" and innovation.

"We declared the war on drugs 40 years ago — the world declared the war on drugs — and it's a war that has not been won. We must be more effective and more efficient," Santos said.

Santos went on to describe steps Colombia has taken to reduce drug violence and trafficking, including offering financial incentives for farmers to produce legal crops instead of coca, which is converted into cocaine. Trump commented that Santos gave "a long and very diplomatic answer."

"I will say it a little bit shorter: walls work," Trump said. "Just ask Israel. They work — believe me, they work — and we have no choice."

The awkward exchange highlighted the shortcomings of Trump's border wall proposal when it comes to drug trafficking. Drug policy experts have contested that a border wall would do little to prevent drugs from coming across the border, as the bulk of illicit substances are stowed away in vehicles that make it into the U.S. through border entry points.

What's more, increased enforcement efforts along the border have led traffickers to adopt creative techniques such as catapults that launch drugs over existing walls, drone deliveries, and intricate tunnel systems. Sanho Tree, director of the Drug Policy Project at the Institute for Policy Studies, told ATTN: in an interview on March 22 that "these new counter-narcotic measures basically create an incentive to find news ways — innovative ways — of penetrating our border security."

By imposing tougher enforcement policies along the border, the government is "rooting out the inefficient traffickers and, conversely, the ones we're missing are the most evolved, the most efficient, the most innovative," Tree said. "We're selectively breeding super-traffickers."