US President Donald Trump has argued that the death penalty is a fitting punishment for drug traffickers heightening the opioid epidemic.

The scourge has torn through the rural and working-class communities that, in large numbers, voted for Trump. And the president, though he has come under criticism for being slow to unveil his plan, has seized on harsh sentences as key to stopping the plague.

"Toughness is the thing that they most fear," Trump said on Monday.

Tough punishment

Trump made his announcement in New Hampshire, a state hit hard by opioids and an early marker for the re-election campaign he has already announced. He called for broadening education and awareness about drug addiction while expanding access to proven treatment and recovery efforts.

But the backbone of his plan is to toughen punishments for those caught trafficking highly addictive drugs.

"This isn't about nice any more," Trump said. "This is about winning a very, very tough problem and if we don't get very tough on these dealers it's not going to happen folks ... I want to win this battle."

The president formalised what he had long mused about: that if a person in the US can get the death penalty or life in prison for shooting one person, a similar punishment should be given to a drug dealer whose product potentially kills thousands.

Death penalty

The Justice Department said the federal death penalty is available for limited drug-related offenses, including violations of the "drug kingpin" provisions in federal law.

It is not clear if the death penalty, even for traffickers whose product causes multiple deaths, would be constitutional. Doug Berman, a law professor at Ohio State University, predicted the issue would go all the way to the United States Supreme Court.

John Blume, a professor and director of Cornell Law School's death penalty programme, said the federal drug kingpin law has yielded few "kingpins" or major dealers, mostly ensnaring mid- to low-level minorities involved in the drug trade.

Criticism

The president's plan drew criticism from some Democrats, including Senator Dick Durbin of Illinois, who said "we can't arrest our way out of the opioid epidemic" and noted that "the war on drugs didn't work in the '80s."

Opioids, including prescription opioids, heroin and synthetic drugs such as fentanyl, killed more than 42,000 people in the US in 2016, more than any other year on record, according to the Centers for Disease Control and Prevention.

Much of what Trump highlighted Monday was largely repackaged ideas he had already endorsed.

He called for a nationwide public awareness campaign, which he announced in the fall, including broadcasting "great commercials" to scare kids away from dabbling in drugs. He announced a new website, www.crisisnextdoor.gov, where members of the public can share stories about the dangers of opioid addiction.

US-Mexico wall

The US president also discussed how his policies, including building a US-Mexico border wall and punishing "sanctuary" cities that refuse to comply with federal immigration authorities, will help reduce the flow of drugs.

Monday was Trump's first visit as president to New Hampshire, which has long occupied a special place in his political rise. He captured his first Republican presidential primary here in 2016, though he narrowly lost in the general election to Democrat Hillary Clinton.

Trump drew criticism last year after leaked transcripts of a telephone conversation with Mexican President Enrique Pena Nieto showed he had described New Hampshire as a "drug-infested den". The Washington Post published the transcripts.

Though the 2020 election is more than 30 months away, early jockeying is already happening in states that play an outsized early role in choosing a party's nominee. Retiring senator for Arizona, Jeff Flake, a persistent Trump critic, visited New Hampshire, which holds the nation's first presidential primary, last week. He told Republicans someone needs to stop Trump - and it could be him if no one steps up.

Meanwhile, the president's daughter, White House Senior Adviser Ivanka Trump, spent Monday discussing infrastructure and workplace development in Iowa, which traditionally holds the first presidential nominating caucus.