Fentanyl, the synthetic opioid responsible for 88 percent of opioid overdose deaths in the United States, is showing up in campaign ads across the country. The message is simple: Fentanyl would disappear if illegal immigration disappeared.

This is wrong. If anything, border crackdowns have exacerbated the crisis.

Much of this narrative places blame on President Biden for less restrictive immigration policies, which have supposedly caused the highly potent fentanyl to “pour across our border.” But this misunderstands the obvious reality about the drug: Because it is so potent, a large supply can be easily concealed. That makes it easy to enter the country through legal border crossings.

Indeed, legal travelers smuggle nearly all fentanyl into the country. It is far easier for one of the approximately 20,000 Border Patrol agents, backed up by 24/7 cameras and aerial surveillance drones, to spot a human being crossing illegally than it is for port inspectors to spot a substance that might be no bigger than a pencil tip in someone’s pockets, baggage or cargo.

The government estimates that it intercepts barely 2 percent of hard drugs entering the country at legal crossing points. At the same time, it estimates that it apprehends about 80 percent of people crossing illegally. Even if that latter number is an overestimation, there would be no reason to cross illegally to bring in fentanyl since doing so legally is much easier.

That explains why 90 percent of fentanyl from Mexico seized in the United States was discovered at legal entry points or interior vehicle checkpoints, not illegal crossing routes. And why barely 0.02 percent of the people arrested by Border Patrol agents possessed any fentanyl.

This also helps explain why 86.3 percent of fentanyl trafficking convictions were of U.S. citizens, not illegal immigrants. It makes sense for the cartels to hire U.S. citizen smugglers because they are subject to the least scrutiny when crossing the border. If it were easier to transport fentanyl by crossing illegally, U.S. citizens wouldn’t be hired for the smuggling jobs.

You might think that maybe what we need is to restrict both legal and illegal crossings. That’s exactly what occurred during the pandemic in 2020 and 2021. The government banned asylum seekers, expelled illegal crossers to Mexico and restricted legal entries only to “essential” travelers. Biden kept the travel restriction until this year, and expulsions to Mexico continue.

Yet that didn’t improve the overdose crisis. Instead, cartels quickly switched from smuggling heroin to the far more dangerous fentanyl, allowing traffickers to supply the same illicit market with far fewer crossings. In those years, fentanyl’s share of the combined heroin-fentanyl border seizures increased from one-third before the pandemic to 90 percent. Fentanyl overdose deaths nearly doubled from 2019 to 2021.

The harsher the crackdown, the more smugglers shift to more potent, easier-to-conceal drugs, such as fentanyl.

This is similar to the unintended consequences of the crackdown on prescription painkillers. Non-medical users who relied on stolen or diverted pills did not stop using opioids as a result of the crackdown; they switched to the more dangerous heroin. Meanwhile, genuine pain patients suffered immensely.

Fentanyl is entering the United States because consumers — almost all of them U.S. citizens — are willing to pay for illicit opioids. As long as there is demand, supply will follow. That’s the lesson of the past century of prohibition — first of alcohol, then drugs. Policymakers must focus on helping people with addictions, not on banning immigration or throwing more taxpayer dollars at ineffective border measures.

How can politicians help? Drug prohibition makes non-medical use dangerous and deadly. If politicians can’t repeal prohibition, they should at least enact proven harm-reduction strategies, including needle exchange and syringe services programs; distributing drug testing equipment such as fentanyl test strips so users can reduce their dose or even discard a drug they got on the street; and making the overdose antidote naloxone widely available over the counter or even in vending machines.

The government should also let physicians treat addiction like any other disease. In the United States, patients often travel miles to take their methadone in front of staffers each day at government-regulated clinics. Lawmakers should let people with addiction receive take-home methadone treatment directly from their doctors, as they have been doing in Britain, Canada and Australia since the 1970s. Politicians should also lift strict quotas on how many patients doctors may treat for addiction using buprenorphine.

Politicians first blamed the drug overdose crisis on physicians and drug companies. Now, they are blaming the problem on immigrants. They’ve blamed everyone but the true culprits: themselves. This November is voters’ next opportunity to hold both parties accountable.