"This isn't about being nice anymore," Trump told the crowd at a New Hampshire event. "These are terrible people, and we have to get tough on those people. We can have all the blue-ribbon committees we want. But if we don't get tough on the drug dealers, we're wasting our time -- just remember that, we're wasting our time -- and that toughness includes the death penalty."
Trump also offered support to policies increasing access to the opioid overdose antidote naloxone, calling for more medication-assisted treatment programs and highlighting a new high-profile advertising campaign to discourage America's youth from trying drugs, similar to the "Just Say No" campaigns from the Reagan era.
However, public health experts roundly condemned the death penalty proposal, with some saying it renews the failed rhetoric from the war on drugs in the 1980s.
"We can't execute our way out of this epidemic," said Dr. Andrew Kolodny, co-director of the Opioid Policy Research Collaborative at Brandeis University. "To be talking about the death penalty sounds to me like a step backwards."
Dr. Guohua Li, a professor of epidemiology and anesthesiology at Columbia University who has studied the epidemic for more than a decade, also cast doubt on the effectiveness of such a policy.
"Criminal justice can play a complementary role in addressing the opioid crisis," Li said, "but relying on the criminal justice system to address public health problems has proven unwise, costly, ineffective and often counterproductive."
The opioid epidemic claimed 64,000 lives in drug overdoses in 2016 and has killed more than 500,000 people since 2000, according to the US Centers for Disease Control and Prevention. Trump has declared the epidemic a public health emergency -- and public health experts said that's where the focus should be.
"Like the epidemics of Ebola and Zika," Li said, "the opioid crisis will ultimately be resolved through a public health approach by public health professionals working in the CDC, state and county health departments, and academic institutions in collaboration with other government agencies and community organizations across society."
In New Hampshire, Trump laid out his vision for tackling the opioid crisis
, saying his approach would be three-pronged: reducing demand through education, cutting off the flow of illicit drugs and saving lives by expanding opportunities for evidence-based addiction treatment.
But he most emphasized that it was time get tough on drug dealers.
"You know it's an amazing thing. Some of these drug dealers will kill thousands of people during their lifetime -- thousands of people -- and destroy many more lives than that," Trump said. "They'll get caught, and they'll get 30 days in jail, or they'll go away for a year, or they'll be fined."
"So if we're not going to get tough on the drug dealers who kill thousands of people and destroy so many people's lives, we are just doing the wrong thing," the president said. "Toughness is the thing they most fear."
His comments were met with applause.
"Whether you are a dealer or doctor or trafficker or a manufacturer, if you break the law and illegally peddle these deadly poisons, we will find you, we will arrest you, and we will hold you accountable."
Trump stressed the death penalty would be sought for the "big pushers, the ones who are really killing people." At one point, he referenced an unspecified country that he claimed doesn't have a drug problem because it has "zero tolerance for drug dealers."
"Take a look at some of those countries," Trump said. "They don't play games. They don't have a drug problem."
However, he acknowledged that the United States may not support this plan. "Maybe our country is not ready for that. It's possible ... and I can understand it," he said. "Maybe, although personally, I can't understand that."
Some of the president's proposals have been endorsed by experts. Naloxone
, the overdose antidote, is extremely effective and can start working in minutes. Harm reduction groups and needle exchanges have been distributing it since 1996, and the CDC says more than 26,000 overdoses have been reversed since then.
Many addiction specialists consider medication-assisted treatment
the gold standard of addiction treatment. It utilizes behavioral therapy as well as medications like buphrenorphine and methadone that can reduce cravings and withdrawal symptoms from opioid use.
A senior White House official said the administration would not be waiting for Congress to propose legislation on the death penalty proposal, saying it is something the Justice Department is "examining to move ahead with to make sure that's done appropriately."
The official declined to give an example of when the death penalty might be used, referring all questions to the Department of Justice. "Obviously, there are instances where that would be appropriate," the official said.
Li said the government's action to impose more severe penalties for drug trafficking crimes is "understandable and, if implemented judiciously and with other more substantive and comprehensive interventions, is likely efficacious." But he cautioned, "the increased penalty by itself, however, is unlikely to make a significant impact on the opioid epidemic."
John Blume, a law professor at Cornell University and director of the university's Death Penalty Project, said the Federal Drug Kingpin Act, which allowed federal prosecutors to seek the death penalty in which a homicide occurred during the commission of a drug transaction, yielded "few kingpins or major dealers -- and mostly ensnared poor, African-American, mid- to low-level persons involved in the drug trade."
"There is no reason to believe this new call for capital punishment in homicide cases for drug dealers will be any more successful," Blume said.
Maria McFarland Sánchez-Moreno, executive director of the Drug Policy Alliance, a nonprofit group that seeks to end the war on drugs, called the policy "deeply cynical."
"There's a lot Trump should be doing; instead, he's resorting to recycled drug war rhetoric, using his usual bombastic approach to rally his base," Sánchez-Moreno said. "It reveals a lack of interest in helping the people who are affected by this crisis, and he's using it for purely political goals."
She said Trump's announcement wasn't surprising, just disappointing. "He's been praising President (Rodrigo) Duterte in the Philippines forever, and that's somebody who advocates going out and murdering people who use drugs," she said.
The Trump administration, she said, needs to "drop its obsession with killing and locking people up and instead focus resources on what works: harm-reduction strategies and access to evidence-based treatment and prevention."
On Twitter, the reaction was similar, with people wondering whether the administration would seek the death penalty for executives at pharmaceutical companies or for doctors at so-called pill mills. Others questioned the logic behind the move.
Dr. Leana Wen, Baltimore City Health Commissioner, echoed that sentiment. "The war on drugs has not worked," she said. "The last thing we need is to further criminalize the disease of addiction. We need for everyone to understand addiction is a disease, that treatment exists and recovery is possible."
What is needed, she said, is tens of billions of new money for the epidemic. "We already know what works," she said. "We just need the funding to get us there."
Kolodny added that it makes some sense to seek stricter penalties for major fentanyl suppliers and pill mill doctors for pushing drugs that can kill, but he said that seeking the death penalty seems to be an overreach.
"The reality is, most people who are selling drugs are suffering from opioid addiction, and they sell drugs to support their own habit," Kolodny said.
"When I start hearing about the death penalty, it just seems to me we're going in the wrong direction."