Republican presidential candidate Donald Trump, surrounded by family and friends, gives the peace sign as he celebrates his victory at a New Hampshire primary campaign watch party at the Executive Court Banquet Facility in Manchester, N.H., on Feb. 9. (Jabin Botsford/The Washington Post)

In his victory speech after the New Hampshire primary, Donald Trump addressed one of the biggest issues facing both the state and nation: heroin addiction, and how he plans to stop it.

"We're going to end it at the southern border," Trump said Tuesday night. "We're going to work like hell to take care of the situation."

Trump and Sen. Ted Cruz (R-Tex.) tell voters that they will end the nation's opiate epidemic by securing the border with Mexico and stopping the flow of drugs to the United States — both have spoken of building a wall between the two countries.

"When the border’s not secure ... you have drugs flooding into this country," Cruz said in New Hampshire last week. He abruptly pivoted to the issue of border security after telling an emotional story about the death of his half-sister from a suspected overdose.

Their intense focus on border security as a way to solve the issue differs from other candidates and from what many researchers and medical professionals believe will halt the epidemic.

"A wall isn't going to stop the flow of heroin because it hasn't in the past and it’s not going to in the future," said Elaine Carey, a professor at St. John's University who has studied drug trafficking.

So what will? Many say a combination of law enforcement and an intense focus on expanding drug treatment to all who need it.

Cruz and Trump are correct that much of the nation's heroin is coming from Mexico. Its cartels have overtaken the nation's heroin trade, deploying what my colleague Todd Frankel called a "sophisticated farm-to-arm supply chain." The cartels are growing and processing their own heroin, even changing the type typically made in Mexico from a viscous, difficult-to-inject drug to one that is easy to snort and shoot, making it more attractive to first-time users. The cartels have gone away from major heroin distribution centers like Chicago and are setting up shop in smaller cities, where users can order drugs by cellphone and have them delivered to their doors. And the drugs aren't just coming over the U.S.-Mexico land border.

"Mexico is a major producer of heroin, but heroin comes in in all different ways to the U.S. It comes in planes, on ships, any way you can possibly think of, in condoms in people’s bodies," Carey said. The supply chain, she said, is like a water balloon — if you squeeze one part the water goes somewhere else. Mexican cartels started pushing heroin after U.S. decrminialization and legalization of marijuana changed the market.

Mexico is also producing a number of other drugs, including methamphetamine and illicit Fentanyl, a potent synthetic painkiller often used to treat pain in cancer patients. Fentanyl is now being mixed into heroin, with deadly results. At least 23 people died of overdoses in Erie County, N.Y., from Jan. 29 to Feb. 10; 19 of those deaths are believed to be from a batch of heroin laced with Fentanyl. In New Hampshire, 151 of the approximately 399 drug overdose deaths in 2015 came from Fentanyl.

Robert L. DuPont, who served as White House drug czar in the 1970s and was the first director of the National Institute on Drug Abuse, said some of the people ferrying drugs from Mexico to the United States are American citizens traveling on legal documents.

"Anybody who thinks that these guys who are swallowing those packets of heroin like that and going through the border with an American passport are going to be easily detected and deterred is crazy," DuPont said.

But the problem, for many, started inside the United States. Many heroin users first got hooked on prescription opiate medication used to treat pain — pills that were was procured in the United States. They are still a major problem and component of the opiate epidemic — each day 44 people die from overdosing on painkillers, according to the Centers for Disease Control. Pills are expensive, and a flood of cheap heroin entered the market, leading many who are addicted to opiates to turn to heroin.

In recent years, law enforcement officials and politicians on both sides of the aisle have come to the consensus that the country will not arrest its way out of the heroin epidemic, and are turning away from more punitive measures used against drug users during the War on Drugs in the 1980s and 1990s. Now prosecutors around the country are trying to go up the supply chain, attempting to prosecute drug dealers and people higher on the supply chain for overdose deaths.

"Supply reduction is essential for public health," DuPont said.

Many law enforcement and elected officials and others are trying to steer users toward treatment — both Cruz and Trump have stressed the need for prevention and treatment. Both have also shared personal stories of addiction — Cruz spoke of his sister's death three times in New Hampshire and Trump told the story of his brother, who died of alcoholism in his 40s.

But in many cases, the demand for treatment outstrips the supply.

For many opiate users, the easiest way to get clean is by going to jail. In many states, there is a lack of treatment beds and funding to create more. Cruz has called for faith-based programs, but did not address what many experts said are crucial elements to solving the problem: naloxone, a drug that reverses opiate overdoses and which many states are giving to law enforcement officers, users and their friends; and medicated-assisted treatment, a practice that some find controversial, where a user takes a prescribed amount of opiate medication under a doctor's supervision. Cruz has called for the expansion of drug courts.

Andrew Kolodny, a senior scientist at Brandeis University's Heller School and chief medical officer at Phoenix House, a national rehab chain, said reducing the number of prescription opiates that are in the hands of the public will also help solve the heroin crisis.

"We have to prevent new people from getting addicted and that’s really boiled down to getting the medical community to prescribe more cautiously," he said.

But for Kolodny and others, the idea that closing the border will stop the flow of heroin is overly simplistic and will not work.

"You can buld a wall and it will come in by boat. Or you have planes drop off in fields. There’s no way to keep it out," Kolodny said.