During his nationally televised Oval Office address Tuesday night, President Donald Trump made the case for more immigration control. Central to his argument was that drugs are flowing into the United States across the southern border. His favored solution: Build the wall.

There's just one problem. Building a wall would do very little to stop drugs from coming into the country. "Our southern border is a pipeline for vast quantities of illegal drugs, including meth, heroin, cocaine, and fentanyl," Trump said. "Every week, 300 of our citizens are killed by heroin alone, 90 percent of which floods across from our southern border."

He's not completely wrong: As The New York Times notes (citing a 2017 National Drug Threat Assessment), most of the heroin smuggled into the country does come in via the southern border with Mexico.

But it's not coming in the knapsacks of border jumpers. "For the first 11 months of the 2018 fiscal year, 90 percent of the heroin intercepted at the border and 88 percent of the cocaine, was captured at a legal port of entry rather than between those ports," USA Today explains, citing Customs and Border Protection data.

Even if the wall gets built, legal ports of entry aren't going away. Most smugglers aren't trying to hop across in the first place; they're trying to sneak contraband by manned border posts. A border wall likely won't change this.

It's also worth noting that, according to the Times, most black market fentanyl comes into the U.S. from China. As Trump's own opioid commission reported in November 2017: "We are losing this fight [against fentanyl] predominately through China."

Trump's attempt to rally support for his border wall by warning of the drugs flowing into the country isn't anything new. He famously kicked off his 2016 campaign by claiming Mexican immigrants were "bringing drugs" into the country.

Conflating the war on illegal immigration with the war on drugs creates a perfect storm for the violation of civil liberties and the expenditure of huge amounts of money, and all for very little gain. Building a wall would involve, among other things, spending tens of billions of dollars and seizing private property. Yet it's an ineffective solution for keeping out both the illegal immigrants and the drugs the president hopes to block.