At the center of the North Korean nuclear crisis is a pivotal question: How much is China really willing to pressure and punish its longtime ally in Pyongyang? Recent conversations in Beijing and Washington suggest that Chinese leaders have decided to increase pressure substantially but are not—and probably never will be—willing to help President Trump strangle North Korea into submission. China doesn’t trust Kim Jong Un—but it trusts Trump even less.

For decades, China backed North Korea in hostilities with the United States. The fellow Communist armies had fought alongside one another in the Korean War, and North Korea still relies on China for as much as ninety per cent of its overseas trade. In Chairman Mao’s analogy, the two nations were as close as “lips and teeth.” But that is no longer true; since taking power, in 2011, Kim Jong Un, who is suspicious of China’s efforts to control North Korea or spur it to follow its model of economic reform, has openly antagonized the government in Beijing, including launching rockets that would embarrass the Chinese leadership. (Earlier this month, Kim fired a rocket just as Xi Jinping, the Chinese President, was opening an annual summit of developing countries in the Chinese city of Xiamen.)

By several measures, Chinese leaders have become more willing to get tough with Kim. Until recently, Chinese intellectuals rarely questioned China’s commitment to North Korea. But, in March, Shen Zhihua, one of China’s best-known experts on the Korean War, said, in a speech, “We must see clearly that China and North Korea are no longer brothers-in-arms, and in the short term there’s no possibility of an improvement in Chinese-North Korean relations.” The speech circulated widely, without much in the way of official censorship—a sign, to many Chinese analysts, that some of the country’s leaders agree.

When I met Shen last month, in Beijing, he told me, “I think more and more leaders share this view. At a minimum, they think that multiple views should exist.” Shen is a calm, silver-haired scholar who works in a research center at East China Normal University, in Shanghai. As a historian, he believes that long-standing tensions between Beijing and Pyongyang are becoming irreparable. “Officially, they tried to paper over the cracks, but the differences were inevitable,” he said.

Shen does not speak for the leadership or advise powerful officials. Rather, his views should be understood as a reflection of the change that is under way in the Chinese establishment. Of North Korea, he said, “I think China doesn’t care who is running the country. Xi and Kim have not met. It used to be a tradition if there is a new leader, to meet him. But not now.” Fundamentally, he said, some have come to believe what was once anathema—that North Korea could one day turn its aggression on China: “Many in China don’t want North Korea to have nuclear weapons because nuclear weapons are, first, threatening to China.”

I wondered if Shen was expressing a minority view. When I met Zhao Tong, who specializes in nuclear issues as a fellow at the Carnegie–Tsinghua Center for Global Policy, I asked him about Shen’s speech. “I think most people would broadly agree,” Zhao said. “It’s not a warm relationship of ‘brothers.’ ” Given that North Korea has continued to test nuclear weapons in the face of Chinese protests, he said, China would not feel automatically compelled to defend North Korea under their mutual-assistance treaty. “Most Chinese would laugh at the proposal that China should provide security guarantees,” he said.

Zhao ticked off examples of China’s new pressures on Pyongyang: “China has stopped coal imports. That’s a big step. It’s stopped supplying diesel and gas. That’s a big step. It has tightened regulations on companies and financial institutions, and the big ones have stopped doing business with North Korea. It’s the smaller ones that are motivated by narrow interests and are still doing business. China has enhanced inspections of goods at the border. They made efforts to help private-sector companies strengthen their export-control practices.”

But, importantly, Zhao added that it would be a mistake to misread those steps as China signing on, wholesale, to American efforts to force North Korea to the edge of collapse—a tactic, favored in Washington, known as “strategic strangulation.” “No, it’s just balancing Trump and Kim Jong Un,” Zhao said. “The reason China agreed to much tougher sanctions is to calm Trump down.” China has strategic tensions of its own with the U.S., so it is keeping both countries off balance. “It’s basically, ‘Who is the bigger evil?’ For China, the U.S. is always the top geostrategic concern, the top threat.”

Zhao notes that the U.N. sanctions against North Korea that were passed on August 5th, which China supported, stopped short of seeking to undermine trade and humanitarian activities. “They are trying to draw a line between North Korea’s military program and civilian trade. To put more pressure on North Korea, without undermining it. China has been taking the incremental approach,” he said. In Zhao’s view, even though China has agreed to limit oil exports to North Korea, it is unlikely to cut them off entirely, which the Trump Administration believes is a vital step to change Kim’s behavior. “If China remains the sole supplier, meaning Russia won’t step in, I think China would find it very hard to do that,” Zhao said.

There are hard limits to China’s willingness to advance American interests in Asia, because the two powers have deep disagreements—about trade, contested territory in the South China Sea, and Taiwan. As the North Korea crisis has escalated, China has urged the U.S. to consider offering North Korea a deal known as “freeze for freeze,” in which the North would halt further tests if the U.S. halts or reduces joint military exercises with South Korea and Japan—exercises that China resents as well. “I think some Chinese are secretly hoping the North Korean position can actually help drive the U.S. forces away from the Korean Peninsula,” Zhao said. “It is in China’s interest if, in the mid-to-long term, the North Koreans can have a deal with the United States where the U.S. reduces troops or reduces its exercises.”

In recent years, overly hopeful U.S. politicians and commentators have repeatedly misunderstood China’s views of North Korea and assumed that Beijing was, at last, turning against its irksome ally. In private meetings with President Obama, and later with President Trump, Xi has repeated a bottom-line principle about North Korea: “No war. No chaos. No nukes.” A former U.S. official, who was at several of those meetings, told me, “Every American senior official that I know hears, ‘Blah, blah, blah—no nuclear weapons.’ And thinks, ‘Oh, we agree! Excellent!’ So the Chinese ought to be willing to limbo under this bar for us. But, no, that’s third in the list of three strategic priorities. The first two are avoiding war on the Korean Peninsula, and avoiding chaos and collapse.” In that spirit, China has sought to limit the scope of U.S.-backed sanctions in the U.N. Security Council. In the latest round, earlier this month, China succeeded in forcing the U.S. to drop its pursuit of a full oil blockade, which China fears would drive North Korea to collapse.

Nothing worries Chinese officials more than the following scenario: the U.S. uses harsh sanctions and covert action—and possibly military strikes—to drive North Korea close to the point of regime collapse. In turn, Pyongyang lashes out with violence against America or its allies, sparking a full-blown war on China’s border, just as China is trying to maintain delicate economic growth and social stability. Xi, in separate sessions, has offered Obama and Trump the same Chinese adage in reference to North Korea: “When a man is barefoot, he doesn’t fear a man with shoes.” In other words, even if attacking America would be suicide for North Korea, if it sees nothing left to lose, it just might do the unthinkable. For that reason, China, above all, wants the U.S. to avoid backing Kim into a corner from which he has no exit.

Trump is fervently seeking China’s coöperation, but, ironically, his rhetoric and aggression may be putting that further out of reach. On Sunday, Trump mocked Kim as the “Rocket Man.” Members of his Administration have repeated their openness to “military options,” despite projections that air strikes, or other attempts at targeted attacks, could spark a wider war. Chinese intellectuals have taken to joking that “Telangpu”—which is one of the Chinese pronunciations of Trump’s name—sounds like “te meipu,” which means clueless or lacking a plan. In recent months, Trump has alternately praised China and threatened it with a trade war. “I don’t understand Trump,” Shen, the historian, told me. “One day he is saying something good about Xi Jinping and the next he is criticizing him. Trump is becoming more and more of a problem. China is becoming more and more stable.”