Evidence mounts that the Chinese government is mightily annoyed with its volatile North Korean ally. Long gone are the days when Chinese officials invariably described the relationship between their country and North Korea as being “as close as lips and teeth.” In a new article in China‑U.S. Focus, I show how the chill in the bilateral relationship has been growing for years and has now reached unprecedented levels. A stark indication was Chinese President Xi Jinping’s recent state visit to South Korea, which became a blatant snub to Pyongyang. Xi did not even bother to stop in the North Korean capital either before or after his summit meeting with South Korean President Park Geun-hye.

The main reason for Beijing’s annoyance has been North Korea’s repeated defiance of China’s warnings not to conduct nuclear tests or missile tests. Both Kim Jong-un and his father and predecessor as North Korea’s supreme leader, Kim Jong-il, ostentatiously ignored Beijing’s admonitions that such conduct was provocative and disruptive. Xi’s courtship of Seoul sends a new warning to Pyongyang that there may be a high price to pay for such defiance.

It also creates an ideal opportunity for the United States to see whether, for the right price, Chinese leaders might be willing to dump North Korea and treat South Korea as its future partner on the Peninsula. Clearly, that would require an even more drastic shift in China’s policy than what has occurred so far. It also would require Washington to make an equally drastic policy change. The core of any deal would be a willingness to withdraw all U.S. forces from the Korean Peninsula and phase-out the defense treaty with Seoul, if Beijing agreed to end its support of North Korea and facilitate Korean unification. Since Washington’s alliance with South Korea is a relic of the Cold War, when Seoul was incapable of providing for its own defense and both Beijing and Moscow firmly backed North Korea militarily, such a concession would not come at the expense of crucial U.S. interests. Today, Seoul has more than enough financial resources to build whatever military capabilities it deems necessary.

There is, of course, no guarantee that Beijing would accept such a deal, but the time is ripe at least to explore that possibility. Chinese leaders are clearly disenchanted with their North Korean ally. We need to find out just how disenchanted, and that requires flexibility and creativity in U.S. foreign policy.