We need a border wall “for one thing,” President Trump claims: “to stop drugs.”

However, as IPS Drug Policy expert Sanho Tree explained to the Bernie Sanders social media team recently, putting a wall on the southern U.S. border could actually make the opioid crisis far deadlier. In the unlikely event the wall stops traffickers from moving heroin into the U.S. from Mexico, Tree says, they’d simply adulterate the existing heroin supply “with even more fentanyl and carfentanil,” two synthetic opioids that are far deadlier than heroin and which are driving a spike in overdose deaths. More likely, though, the wall would be easily circumvented.

Tree links the wall to a broader, failed approach of criminalizing drug use. Instead, he points to a more systemic diagnosis. The opioid epidemic “is a complex crisis driven by poverty, despair, and alienation,” he concludes, “and we are not going to arrest our way out of this problem.”

Sanho Tree directs the Drug Policy Project at the Institute for Policy Studies.