Mr. Trump seems so enamored with autocrats and strongmen that he wants the United States to imitate governments like China and the Philippines by executing drug dealers, claiming such countries “don’t have a drug problem” because of their brutality. This is patently absurd. While it is hard to analyze the experience of many of these countries because they do not collect and publish reliable data about substance use, experts say it is clear that they have not eliminated drug abuse or the crime that often accompanies it. More broadly speaking, many scholars have concluded that there is no good evidence that capital punishment deters crime.

But we do have convincing evidence that ratcheting up the war on drugs, as Mr. Trump and his attorney general, Jeff Sessions, want to do, would not work. Since the early 1980s, the federal government and states have imposed increasingly harsh criminal penalties on drug dealers and users. Not only did they fail to stem drug use or the availability of illicit substances, but they may have contributed to their spread by taking resources away from treatment and prevention efforts. It is no wonder, then, that the per-gram retail price of heroin fell by about 85 percent between 1981 and 2012, according to a report published in 2016 by the White House Office of National Drug Control Policy.

Further, legal experts say it is unlikely that a law authorizing capital punishment for drug dealers would be considered constitutional, because the Supreme Court has previously struck down laws that allowed the use of the death penalty for crimes other than murder.

Mr. Trump’s other get-tough policies are also unlikely to help. The wall will not stop drugs — most imported illicit substances like heroin and methamphetamines already come in through legal border crossings. And his plans to penalize sanctuary cities, which choose not to participate in federal deportation crackdowns, would be counterproductive. That’s because law-abiding immigrants are less likely to identify and testify against drug dealers and gang members if they fear that helping law enforcement agencies could put them or their relatives at risk of being detained or deported.