Philippine President Rodrigo Duterte delivers his first state of the nation address, in suburban Quezon City, northeast of Manila, on July 25. (Bullit Marquez/Associated Press)

RODRIGO DUTERTE, the new president of the Philippines, is overseeing exactly what he pledged in his campaign: a terrifying surge of extrajudicial killings of suspected drug dealers, users and criminals. From the day after he was elected, May 10, to Aug. 4, by a local account, there had been 571 killings, most of them simple executions by police and vigilante groups. Mr. Duterte promised to “shoot to kill” and eliminate drug dealing in the country in six months. In fact, he is killing the rule of law, and that could undermine Philippine democracy.

Mr. Duterte declared in his inaugural speech that his “adherence to due process and the rule of law is uncompromising.” But later that day, after taking the oath, Mr. Duterte visited a Manila slum and told a crowd, referring to drug dealers, “These sons of whores are destroying our children. I warn you, don’t go into that, even if you’re a policeman, because I will really kill you. If you know of any addicts, go ahead and kill them yourself, as getting their parents to do it would be too painful.”

The Philippines has a serious drug problem, chiefly with crystal meth, a.k.a. shabu. The drug trade took root in a nation plagued by rampant corruption and a discredited political establishment. Mr. Duterte’s firebrand response to drugs has been popular. But the street executions are taking lives without trials or proof of criminality. Drug addicts and abusers who need medical attention and counseling are getting a bullet instead. Police have claimed suspects resisted arrest or shot at them but have provided no evidence. More than 300 organizations involved in issues related to drug production, trafficking and use have appealed to international drug-control agencies to help stop the killings and to tell Mr. Duterte that they “do not constitute acceptable drug control measures.” That’s putting it mildly.

No one should be surprised by Mr. Duterte’s brutal tactics. He has been championing extrajudicial violence for nearly two decades. From 1998 until this year he served as mayor of Davao City on the main southern island of Mindanao, where death squads took the lives of more than 1,000 people. An investigation in 2009 by Human Rights Watch documented the grisly methods of the killers; they meted out summary executions with impunity. On May 24, 2015, in a television broadcast, Mr. Duterte identified with the shadowy killers. “Am I the death squad? True. That is true,” he said. He pledged that if elected president, he would execute100,000 criminals and dump their bodies in Manila Bay.

The past few weeks provide grim foreshadowing that he may be serious about that. Mr. Duterte won the election as a profane, take-no-prisoners leader who did not bristle at the word “dictator.” While the persona may have proved effective in the campaign, a real dictator, especially one with blood on his hands, is hardly what the Philippines needs.