In a speech before law enforcement leaders this week, President Trump vowed to be “ruthless” in the fight against drugs that are “poisoning our people.” Trump's comments represent a sharp departure from the Obama administration, which publicly disavowed the harsh anti-drug rhetoric of previous decades in an effort to emphasize treatment of drug users over punishment.

“We're going to stop the drugs from pouring in,” Trump told the assembled members of the Major Cities Chiefs Association on Wednesday. “We're going to stop those drugs from poisoning our youth, from poisoning our people. We're going to be ruthless in that fight. We have no choice. And we're going to take that fight to the drug cartels and work to liberate our communities from their terrible grip of violence.”

Aside from the cartels, Trump did not elaborate on who would be at the receiving end of that ruthlessness. In a campaign speech in New Hampshire last October, Trump outlined the drug control policies he supported, including expanded treatment options for drug users and better access to anti-overdose drugs.

He also called for increasing mandatory minimum prison sentences for “the most serious” drug offenders, aggressive prosecution of drug traffickers, and cracking down on “shipping loopholes” that he said allowed countries such as China to send dangerous drugs to the United States via the Postal Service.

In that speech, Trump also criticized the Obama administration for commuting the sentences of “record numbers of high level drug traffickers, many of them kingpins.” He said continuing that strategy would amount to “turning our streets back over to gangs, drug cartels, and armed career criminals.”

“This rhetoric is dangerous, disturbing, and dishonest,” Ethan Nadelmann, executive director of the Drug Policy Alliance, said in a statement. “History has taught us that cracking down on drugs and building walls will not stop the supply or use of drugs. It mostly causes the death and destruction of innocent lives.”

The White House did not respond to repeated requests for comment.

Nearly 80 percent of Americans favor eliminating mandatory minimum drug sentences like the ones Trump called for expanding.

A 2014 Pew Research Center survey showed that Americans strongly prefer treating drug users over incarcerating them, 3 to 1. But federal policy has been slow to reflect that preference.

In the past decade, federal focus has shifted somewhat from “supply-side” anti-drug policies — seizing drug shipments, incarcerating dealers and arresting drug users — toward a more “demand-side” approach that uses substance abuse treatment and prevention programs to stop people from using or becoming addicted to drugs in the first place.

“Ruthlessness is a great virtue for a gangster or a warlord,” said drug policy expert Mark Kleiman of New York University. “Not so useful for the leader of a republic.”

Many public health experts agree that the “war on drugs” was a failure. The thinking behind supply-side drug policies is that by reducing the supply of drugs they become more expensive, and therefore less likely to be used and abused. But a 2013 study in the British Medical Journal found that since 1990, drug prices have decreased while drug purity has increased, making it easier and more affordable than ever to get high.

“These findings suggest that expanding efforts at controlling the global illegal drug market through law enforcement are failing,” the authors conclude.

From 1991 through 2001, when many of these supply-side policies were in full force, the rate of illicit drug use among American teenagers increased sharply. Over the same period, the rate of teen cigarette use fell slightly, and the rate of underage alcohol consumption dropped sharply.

From a public health standpoint, the primary difference between illicit drugs, alcohol and tobacco is that the latter two substances are legal for adult use.

A number of experts believe supply-side drug policies can be effective if used judiciously and in conjunction with other policies.

“We overlearned the lesson that supply control doesn't work and failed to apply it to prescription opioids when we should have,” Jonathan Caulkins of Carnegie Mellon University said in an interview. He said he believes this contributed to the federal government's inadequate response to “pill mills and other criminal excesses in the supply of prescription opioids.”