At a speech today with Maine Gov. Paul LePage (R), Republican front-runner Donald Trump blamed lax southern border security for the state's heroin problem and claimed his planned border wall would be the solution.

"The wall is gonna stop drugs coming into Maine, New Hampshire," the presidential candidate told the crowd.

Trump is partially correct about the southern border's role in drug trafficking. According to numbers from U.S. Customs and Border Protection, most of the heroin seized in the United States is caught at the southern border. A negligible amount is stopped at the Canadian border.

But a not-insignificant percentage of heroin is trafficked via plane and seized at U.S. airports. In 2014, for instance, border officials seized more than 800 pounds of heroin at airports in the United States.

More to the point, if experts have learned anything from the shortcomings of the drug war over the past 30 years, it's that attempts to cut off the supply of illicit drugs do little to address the drug problem if demand remains high. In the case of heroin, policymakers tried to cut the supply of the drug by, among other things, eradicating opium crops in Afghanistan and arresting dealers

But they did nothing to address underlying demand. As a result, the percentage of Americans using heroin has hardly budged since 1979. And the price of heroin (in inflation-adjusted dollars) plummeted during that same period, which is generally seen as an indicator that the drug became easier to get.

Beefing up heroin enforcement along the southern border likely won't stop the flow of heroin into the United States. Traffickers will simply move their product via other means. They may increase their efforts to smuggle via other channels, like airports. They may reroute their product through Canada. They may start shipping more drugs via Priority Mail. They may resort to submarines, drones, and other outlandish conveyances that authorities haven't even thought of yet.

Trump's promise to prevent drugs from entering the country in the first place is a throwback to the drug war policies of previous decades. This may be no accident. He recently sought drug policy advice from William J. Bennett and discussed the heroin epidemic with him. Bennett served as the nation's first Drug Czar in the late 80s and has remained a proponent of harsh 1980s-style drug war tactics. He recently co-authored an op-ed entitled "Bring Back the War on Drugs."

If Thursday's speech is any indication, Trump may be taking that message to heart.

What Donald Trump is doing on the campaign trail

U.S. Republican presidential nominee Donald Trump speaks at a campaign event at Trump Doral golf course in Miami, Florida, U.S. July 27, 2016. REUTERS/Carlo Allegri (Carlo Allegri/Reuters)