Even when President Trump has a good idea, he doesn’t stick with it long enough. Like pushing China on North Korea.

Of North Korea, said candidate Trump: “We should put pressure on China to solve the problem.” As president, he initially placed the issue front and center in the U.S.-China relationship.

But a couple months later, Trump appears to have lost hope in Beijing. “While I greatly appreciate the efforts of President Xi & China to help with North Korea, it has not worked out. At least I know China tried,” he tweeted recently.

A Chinese Foreign Ministry spokesman responded that his nation had “played an important and constructive role” in promoting peace on the Korean peninsula. Exactly how the People’s Republic of China helped is not clear, however. It cut back on coal purchases, but other commerce with North Korea continues. The Trump administration asked the Xi government to act against ten firms and individuals who trade with the North, but is still waiting for action.

Most proponents of “the China card” imagine Beijing cutting off trade, especially energy and food. Having just returned from Pyongyang — the North Korean government invited me but the Cato Institute paid my expenses — I found both energy and food to be in seeming good supply. Despite reports that gasoline prices have increased, there was no visual evidence of a shortage.

An undefined diplomatic duty won’t prompt China to act. The Trump administration must therefore convince Xi’s government that punishing North Korea benefits China. Which means Washington must take into account Beijing’s interests.

First, Chinese officials have long blamed the U.S. for adopting a threatening policy, which spurred the North to build nuclear weapons. Thus, Washington should work with South Korea and Japan to develop a package of benefits — economic assistance, security assurances, peace treaty, diplomatic recognition, and more — to offer in return for denuclearization, and present it to Beijing, then to the Democratic People’s Republic of Korea.

Second, China fears a messy collapse if the DPRK refuses to disarm. Nightmares of millions of refugees crossing the Yalu River, factional conflict in Pyongyang, combat among competing military units spilling across the border, and loose nukes have created a strong Chinese preference for the status quo. The U.S. needs to emphasize that the present situation is also dangerous and discuss how the allies are prepared to assist with any ill consequences. A commitment to help care for refugees and accept Chinese intervention in the North, for instance, might help assuage Beijing’s concerns.

Third, Beijing does not want to facilitate Korean reunification, creating a larger and stronger state allied with the U.S. and leaving American troops on the Yalu, or even farther down the peninsula. Among the issues worth discussing: respect for Chinese economic interests in North Korea, withdrawal of U.S. forces after reunification, and military nonalignment of a unified Korea.

Fourth, the U.S. could offer additional positive incentives. Trade, Taiwan, and territorial issues all provide areas where Washington could offer specific concessions in return for Beijing’s assistance. That obviously would increase the price of any agreement, but the U.S. has to decide how far it will go to promote denuclearization.

Of course, such an approach leaves much to be desired. Even if Kim Jong Un’s government accepted benefits in exchange for disarmament, human rights abuses could still continue. Or Pyongyang might refuse and survive, leaving an even more dangerous and impoverished nuclear nation. In the event of government collapse, China might resurrect the DPRK, only with more pliable rulers.

However, there are no better options. Military strikes might not destroy the North’s main nuclear assets and probably would trigger a second Korean War, which would result in horrific death and destruction even for the “victors.” Targeting Chinese firms would damage relations with Beijing without necessarily significantly weakening Pyongyang. People look longingly to Beijing only because enlisting China’s help appears to be the best of several bad options.

If there ever were a time for the U.S. to negotiate for Chinese cooperation, it is now. Trump and Xi appear to have established a positive relationship. The tragic death of Otto Warmbier after his release by Pyongyang adds urgency to efforts to address North Korea. Moreover, in Pyongyang I saw no visible signs of the warm friendship that officially exists between North Korea and China. In fact, North Korean officials said they wanted to reduce their dependence on “any one nation.”

Winning Chinese assistance remains a long shot, but Trump should put his self-proclaimed negotiating skills to work. There is no alternative, other than essentially accepting North Korea as a nuclear state, which the president presumably does not want as his foreign policy legacy.