North Korea has conducted its third nuclear test. Its action was the equivalent of an upraised finger to virtually every other nation. But it was aimed most directly and clearly at China , Pyongyang’s nominal ally. The United States should use the North’s latest provocation to challenge Beijing to do more to constrain the so-called Democratic People’s Republic of Korea.

China claims to be upset. Foreign Minister Yang Jiechi told the North Korean ambassador that the People’s Republic of China was “strongly dissatisfied and resolutely opposed” to the nuclear test. Yang also urged the DPRK “to honor its commitment to denuclearization and not to take action that may worsen the situation.” He insisted that the North “return to the right course of dialogue and consultation as soon as possible.”

The irritation almost certainly is real. But we’ve heard all this before. Whenever Pyongyang has tested a nuclear weapon or missile, Beijing has criticized its ally. Sometimes, as after the North’s most recent rocket launch, China has even approved a UN Security Council resolution penalizing North Korea.

And then nothing has happened—until the next North Korean missile or nuclear test. Indeed, even as Pyongyang has grown more provocative, sinking a South Korean warship and bombarding a South Korean island in 2010, the PRC has expanded its economic ties with the DPRK. Chinese officials undoubtedly wish their Korean dependent was less headstrong, but they long ago decided that the risks of attempting to modify Pyongyang’s behavior were too great.

Could this be the moment when the Beijing changes course? Zhu Zeng of Peking University told the Washington Post: “The nuclear test of North Korea this time will push China to rethink.” In the past, Zhu claimed, the PRC believed that communication could resolve the controversy. However, “this time, North Korea showed their determination and hard line to own nuclear weapons, which is not negotiable.” The semiofficial Global Times ran editorials proclaiming that the North would “pay a heavy price” and could face an aid cutoff.

But the DPRK’s nuclear determination long has been evident. The depressing history of provocations, tests, and broken agreements suggests that the North set its course well before now. The United States made important mistakes along the way which may have reduced chances for a solution, but having come this far it is hard to imagine that Pyongyang is prepared to give up the one weapon which guarantees the state’s security, provides the regime with prestige, offers an opportunity for international extortion, and rewards the military, the domestic political player with the most guns.

Even Zhu, who believed that the relationship between Beijing and Pyongyang is changing, said he doubted “that China will announce any unilateral sanction toward North Korea.” The PRC’s fear of instability is simply too strong.

However, Beijing’s credibility fades with every new DPRK provocation. No doubt Pyongyang expects a tongue-lashing but no more. If China obliges the North once again the latter will be even less likely to heed the PRC in the future.

So now is the time to play the China card, about the last option in the Korean geopolitical game. Military strikes would risk triggering a full-scale war. Sanctions so far have failed and are guaranteed to fail without Chinese support. Diplomacy has yielded short-term hope but long-term frustration.

Almost everyone sees the PRC as the answer. To the extent anyone has influence in Pyongyang, it is China. Moreover, Beijing provides the bulk of food and energy assistance, as well as foreign investment and trade, with the North. Cutting these ties would inflict immense pain on the North Korean economy.

Still, the DPRK’s leadership would not go quietly. Observed Stephanie Kleine-Ahlbrandt of the International Crisis Group: “North Korean resentment of China is at a high now. The more they depend on China, the more they resent China.” Whether the Kim regime would concede or stand firm, or be overthrown, perhaps by military or political factions allied with the PRC, is impossible to predict. But a serious Chinese push for reform or regime change might yield results.

However, the PRC is not likely to act without a push from North Korea’s neighbors. And Beijing would have to be convinced that acting is in its interest, not just in that of America, South Korea, or Japan.

China values its historic ties with the North and enjoys some economic gain from their commercial relations. However, the PRC’s most important objectives in the North appear to be essentially negative: forestalling a messy, even violent implosion next door and preventing creation of a reunified Korea allied with America on its border.

First, Washington, Seoul and Tokyo need to work together to convince China that these perceived benefits are illusory. The current situation is highly unstable. The DPRK may not want war, but the Kim regime could easily go one provocation too far. Surely Beijing could understand why South Korea and Japan would find it hard to calmly accept a nuclear North Korea. Indeed, if Pyongyang continues on its current course, Washington might decide that it would be better for its allies to develop countervailing nuclear weapons than to forever shield the South and Japan. Then the PRC would share the nightmare of proliferation in Northeast Asia.

Second, the United States, South Korea and Japan could offer to share the cost of any North Korean collapse and accept the prospect of temporary Chinese military intervention to help maintain order. Moreover, Seoul and Washington should assure Beijing that all American troops would go home after reunification. There would be no U.S. military garrison on China’s border.

Third, the United States should work with the North’s neighbors to develop a comprehensive settlement, trading verifiable denuclearization with economic and political engagement and security guarantees. Washington should share the program with the PRC, seeking the latter’s support. Then a “Godfather” offer could be made to Pyongyang: take the deal or accept isolation even from China.

Who knows how the DPRK would respond? However, the starting point would be to get the PRC to cooperate. And that would require a sustained diplomatic effort that appeals to Beijing’s long-term interests. Making the sale would be difficult. However, North Korea may have made the task a little easier by dissing China yet again. If Beijing refuses to act now, it will end up as Mao Zedong’s famous “paper tiger.”