When President Trump makes his case tonight that there really is a border crisis, he’ll probably mention the opioid epidemic ravaging the United States, which killed thousands of Americans last year. Trump and his surrogates often cite the drug crisis as a reason the border wall with Mexico is needed.

There is a “massive influx of drugs that come across the southern border,” White House press secretary Sarah Sanders said Sunday during an interview on Fox News. “Ninety percent of the heroin that comes into this country comes across through the southern border and 300 Americans are killed from that every single month,” she told Fox’s Chris Wallace.

Sanders is correct that most of the heroin in the United States comes from Mexico, according to the Drug Enforcement Administration’s 2018 annual drug threat assessment.

But it’s exceedingly unlikely that a wall will keep the drugs out.

“Drug trafficking businesses are very nimble organizations,” said Elaine Carey, dean of the College of Humanities, Education and Social Sciences at Purdue University. “The way opioids flow or any drug or narcotic, it’s from all different ways. Yes, it comes across the border, but it comes through airports, ships, on trucks, too. A wall’s not going to do anything unless you deal with the demand.”

Most heroin coming into the country is not illegally smuggled in but rather driven across in privately owned vehicles at “legal ports of entry, followed by tractor-trailers, where the heroin is co-mingled with legal goods. Body carriers represent a smaller percentage of the heroin movement and they typically smuggle amounts ranging from three to six pounds taped to their torso, or in shoes and backpacks,” according to the DEA report.

The most dangerous opioid, fentanyl, can be ordered online and shipped from China via the U.S. Post Office. (That hasn’t stopped conservatives like Ann Coulter from tweeting “100% of heroin/fentanyl epidemic is because we don’t have a WALL,” a comment rated as “Pants on Fire” by PolitiFact.)

The Post’s own Fact Checkers gave Trump “Four Pinocchios” for his repeated claims that a border wall is a solution to stopping drugs from Mexico, which he’s been saying since the 2016 campaign. They point out that as far as the opioid crisis is concerned, Trump’s own commission mandated to find ways to combat the epidemic did not mention an open border as a culprit and instead said new heroin users are getting hooked largely because they get addicted to prescription pain medications,

Democrats have jumped on Trump for this, arguing the money he wants for the wall would be better spent investing in technologies that could detect the drugs.

But Carey said even doing that would be failing to attack the problem at its root, which is demand for the product. “If we build the wall, demand is still going to be there,” she said.

Trying to curb drugs coming into America isn’t about cutting off the supply, it’s about cutting off demand through funding for prevention and recovery programs, which public health experts have long argued is the only way to overcome the epidemic.

While few people believe the government has done enough to tackle the crisis, there are programs that do this and even more so after Congress passed legislation last fall to address the opioids issue.

The remarkable irony is that some of that work that would actually help Americans struggling from the opioid crisis could be stalled because the government is shut down. Politico reported that “many key staff in charge of coordinating the Trump administration’s response to the opioid crisis have been furloughed.”

The aforementioned Fact Checkers created this handy cheat sheet to use when listening to Trump’s immigration address to fact-check his claims in real time.