We shouldn’t be surprised by the coarseness spewing from Philippine President Rodrigo Duterte, who insulted President Obama by calling him a “son of a whore.” Vulgarity is Duterte’s calling card. Miffed at the traffic jam that Pope Francis’ visit to Manila caused in 2015, he called the pontiff exactly what he called Obama. He also once said he would castrate men who did not go along with his plan for mass vasectomies to deal with overpopulation. And at an election rally last spring, he joked about not getting a chance to rape an Australian woman, a missionary who in 1989 had been taken hostage, raped and killed during a prison riot.

What’s more worrisome about Duterte is how he has overseen a vicious campaign of extrajudicial killings in the name of waging war against Philippine drug dealers and addicts. Local estimates put the number of people killed in his drug war at 2,400 in a span of two months. Police and vigilante groups are carrying out street executions, embracing what Duterte labeled his “shoot to kill” approach to drug dealing and drug use. The 71-year-old leader took office earlier this summer and hasn’t been vague about his intent, telling a crowd in a Manila slum on the day of his inauguration, “If you know of any addicts, go ahead and kill them yourself, as getting their parents to do it would be too painful.”

Obama was right to respond to Duterte’s intemperate babbling at an Asian summit in Laos by canceling a bilateral meeting with the Philippine leader, who now says he regretted what he said. (The two informally met Wednesday at a dinner of world leaders and exchanged niceties.) But long after the summit, the U.S. faces a much trickier task in dealing with the Philippine leader. How hard should the U.S. come down on a government that jettisons due process, yet also serves as a vital ally in American policy toward China?

We think the answer is simple: The U.S. should get tough with Duterte. His bombastic populism has endeared him to a nation wearied by establishment politics and fed up with drug crime. But Filipinos for the most part are ardently pro-United States. Duterte’s brutal drug war may be popular with Filipinos, but alienating the U.S. likely won’t be. That’s leverage Washington can use as it looks for ways to pressure Duterte to carry out his fight against drugs through lawful arrests and fair trials.

Filipinos know how vital the U.S. is to their effort to keep China from commandeering a crucial swath of the Pacific. China has been creating artificial islands in the South China Sea to justify its claim to territorial waters there — a charade declared illegitimate by an international tribunal in July in The Hague. Under Duterte’s predecessor, Benigno Aquino III, Manila bolstered an already strong military alliance with the U.S. as a counterpoint to China’s actions in the South China Sea, allowing Washington to build military facilities at five Philippine bases.

Duterte has his own ideas about the South China Sea dispute, including the possibility of giving in to China’s claim in exchange for China building a new rail line on the island of Mindanao, where Duterte is from. That may not sit well with the majority of Filipinos, given their wariness of China’s actions.

We’ve seen Duterte’s kind before — around the globe, presidential candidates often build election campaigns on reckless populist rhetoric. While Duterte’s gutter talk is meant almost exclusively for domestic consumption, his lack of regard for human rights is something the West, and the U.S. in particular, shouldn’t and can’t ignore.