President Trump told reporters on Air Force One on Wednesday that his proposed border wall would have to be “transparent” to prevent Americans from being struck and killed by 60-pound sacks of drugs tossed over from the Mexican side.

“One of the things with the wall is you need transparency. You have to be able to see through it,” Trump said. He continued:

In other words, if you can't see through that wall -- so it could be a steel wall with openings, but you have to have openings because you have to see what's on the other side of the wall. And I'll give you an example. As horrible as it sounds, when they throw the large sacks of drugs over, and if you have people on the other side of the wall, you don't see them -- they hit you on the head with 60 pounds of stuff? It's over. As crazy as that sounds, you need transparency through that wall.

Trump acknowledges that the scenario he paints is somewhat “crazy,” but there is a kernel of truth to it. For decades, drug smugglers have employed an arsenal of sometimes cartoonish tactics — from tricycles to narco-subs to drone delivery — to ferry their wares north of the border.

One such tool is the drug catapult — or more accurately, the drug trebuchet: a medieval-era device capable of slinging heavy objects, typically marijuana bales, across hundreds of yards. Due to their outlandishness, they typically make a splash in the national news when one is seized, as one did this past February.

SUNY-Albany homeland security expert Brandon Behlendorf told Wired this week that it's nearly impossible to design a wall tall or “transparent” enough to stop a well-built trebuchet.

“They’re launching drugs not five feet from the wall, or 10 feet from the wall, where a transparent wall would help,” Behlendorf said. “They’re launching it 100 feet over the wall, 150 feet over the wall. No amount of transparency is going to help you in that context.”

Trump's proposed wall is part of his plan to restrict illegal immigration, but he has also cast it as part of a solution to drug abuse and overdose deaths. “The Wall is a very important tool in stopping drugs from pouring into our country and poisoning our youth (and many others)!" he wrote on Twitter in April. “If the wall is not built, which it will be, the drug situation will NEVER be fixed the way it should be!”

[Trump says he wasn't joking about a solar-paneled border wall]

But his remarks to reporters amount to an admission of something drug and security experts have been saying all along: The wall will do nothing to stop the flow of drugs. The bulk of drugs will continue to flow through existing border checkpoints. In more remote areas, smugglers will tunnel under the wall. They'll climb or fly over it.

“There are simply too many alternative ways of moving drugs into the country to justify a wall,” said Sanho Tree, director of the Drug Policy Project at the Institute for Policy Studies, in April.

But Trump, despite acknowledging that drugs will continue to cross the border after any wall is built, remains undeterred. “We have some incredible designs” for it, he told reporters this week.

Need more trebuchets and flying drugs? Read this from our colleague Philip Bump.