President Trump believes the road to disarming North Korea runs through China, its biggest and most powerful ally. The problem is that Beijing doesn't seem willing to do much of anything to rein Pyongyang in.

Trump is right that China is indispensable to North Korea’s economy and serves as its biggest shield against international efforts to end its nuclear program. Unless Trump wants to pursue a potentially catastrophic military strike on North Korea, Beijing features front and center in any political answer to what is rapidly emerging as the most dangerous foreign policy challenge of Trump’s young presidency.

Tensions have been rising between the US and North Korea at an astonishing clip. In the past week, North Korea has held a massive military parade, attempted (unsuccessfully) to fire off yet another ballistic missile, and threatened nuclear war with the US. And it seems prepared to take an even more provocative step: US officials believe Pyongyang is preparing to carry out a nuclear test, something Beijing has repeatedly urged it not do.

Trump has been a bit vague on exactly what he wants China to do, but we have a sense of the broad ideas. He wants it to take the gloves off and move beyond the relatively modest pressure tactics it’s applied so far to the dictatorship, many of which have focused on causing discomfort to elites, such as banning the flow of luxury goods into the country. That would mean dramatically increasing pressure on the nation’s economy as a whole through measures like shrinking trade or cutting off oil shipments.

Analysts say the world has not hit North Korea with the kinds of harsh sanctions that had been slapped on Iran in the past because of its own nuclear program. Some of them believe that if Washington and its allies ratchet the pressure high enough, Pyongyang will be forced to choose between its weapons program and economic survival — and ultimately choose the latter in a bid for self-preservation.

But convincing China to get on board with aggressive economic policies is a toweringly tall order. That’s because Beijing has a vested interest in a stable North Korea — and will drag its heels as much as it can on measures that could destabilize the country. That’s something that was plainly apparent during a meeting at the Chinese Embassy on Wednesday, when Chinese officials repeatedly told reporters that they’re not planning to use any big economic sticks to force North Korea to come to heel.

China sees North Korea as more of an asset than a liability

While South Korea, Japan, and the United States are worried about the possibility of North Korea firing nuclear missiles at them, or using the threat of an attack to blackmail them, China has no such anxiety about its neighbor. North Korea needs China for its economic survival and to keep it safe from serious international pressure; there's no chance it would risk a military confrontation of any kind.

What may be less intuitive, however, is that China sees North Korea as a shield of sorts as well. That’s crucial to understanding why Beijing has been reluctant to lean too hard on North Korea with economically punishing measures to end its nuclear and missile programs.

If Kim Jong Un’s regime were to fall apart, it would cause chaos and likely send millions of poor, starving North Koreans fleeing over the border into China. It also could lead the US to increase its military presence in the region while deploying special forces to secure the North’s nuclear weapons.

Beijing has even bigger strategic concerns when it looks down the road. North Korea’s hermit kingdom stands between China and the affluent democracy of South Korea. China likes the fact that South Korea’s potentially alluring alternative to its own style of governance and economic management doesn’t actually run up against its borders.

But if North Korea were to collapse and the Korean Peninsula became united again under Seoul’s control, that alternative model would be right on China’s doorstep.

Yet a united Korea wouldn’t simply expand Seoul’s power and make it a fiercer competitor with China — it would also boost the reach of its allies. South Korea has a deep alliance with the US, whose sphere of influence would then also run right up to China’s borders. The US has nearly 30,000 troops stationed in South Korea, and it could park even more there under a united Korea.

In addition to all this, China also has a kind of politico-cultural sympathy for North Korea’s current lot in life. “China sees North Korea and sees a backward country, under threat from the US, and they see their own past,” Bonnie Glaser, the director of the China Power Project at the Center for Strategic and international Studies, told me. “They know the history of their own country was to transform itself from a closed, isolated country to one that was open economically, and had tremendous success.”

In Beijing’s ideal scenario, North Korea would follow in China’s footsteps, taking steps toward a market economy and creating modest openings in civil society. Robert Kelly, a professor of international relations at Pusan National University in South Korea, said that China would ideally like to see North Korea evolve into a post-communist reformist dictatorship that resembles a country like Vietnam.

China has long encouraged that course. But so far, Pyongyang has shown relatively little interest in reintegrating itself into the world, and appears fixated on developing nuclear weapons with as much fanfare as possible.

So China is caught in a bind. It wants a stable North Korea. But the North’s aggressive rhetoric and continued ballistic missile tests — to say nothing of a possible nuclear test — are making the international community inclined toward far-reaching sanctions that could destabilize North Korea by crippling its economy. And a military confrontation would also cause the kind of chaos China wants to avoid.

That leaves China feeling that it has to do something. But it seems willing to do far, far less than what the US would want.

China wants small steps on North Korea

So far, China has preferred to thread the needle with targeted measures against North Korea to discourage its nuclear weapons program and missile testing. Since North Korea’s first nuclear test in 2006, the United Nations Security Council has been imposing different kinds of sanctions on Pyongyang. China, which is a permanent member of the council, has been very involved in the negotiations on the wording of the resolutions — and has generally sought to water them down to ensure they aren’t too hard-hitting.

Currently there’s a range of UN sanctions in place against North Korea. They include, among other measures, an arms embargo, limitations on purchasing coal and minerals from North Korea, a ban on supplying luxury items to the country, and the prohibition of financial services that specifically help North Korea’s banned nuclear and missile programs.

As North Korea’s missile testing has become more aggressive in recent months, China’s patience appears to be growing thinner — and its pushback against North Korea appears to be growing more substantial.

In response to a ballistic missile test in February, China announced that it would suspend all coal imports from North Korea for the rest of the year — a firm move in accordance with the UN’s resolution’s goal of curbing the country’s coal sales.

Chinese media has been escalating criticism of North Korea, hinting at harsh consequences for Pyongyang if it continues to defy international norms.

And Glaser says that recently China has gone above and beyond the UN’s call of duty — there’s been an “apparent shutdown of Chinese group tours going to North Korea and apparent suspension of Air China flights to Pyongyang.”

But the key word there is “apparent” — China often says it’s going to take some kind of measure against North Korea but then doesn’t actually deliver.

Chinese officials sounded resolute that China’s relationship with North Korea would hew closely to the status quo

Consider the fact that it’s obvious China doesn’t enforce the UN limits on luxury goods flowing into North Korea — items that Pyongyang’s elite love but can’t obtain domestically. Glaser says she’s seen evidence of poor enforcement when personally witnessing Mercedes-Benz cars drive across the China–North Korean border without license plates.

While China’s recent announcement on suspending coal imports from North Korea sounds bold, in the very recent past it has surpassed the limits imposed by UN caps. And as Troy Stangarone of the Korea Economic Institute of America has pointed out, it’s possible China was already so close to hitting the limit this year that the suspension was bound to happen within months — regardless of Pyongyang’s missile testing. Kelly, the Pusan professor, also says it’s worth considering that small dealers on the border could end up circumventing the suspension of sales. In other words, it’s too early to read China’s move on coal as a big deal.

It’s hard to see China dropping the status quo anytime soon

So what could China actually do to show it means business? One big move would be to cut down dramatically on the overall volume of trade it does with North Korea, which makes up an overwhelming majority of the trade the country does with the outside world. The other big move is to cut off the hundreds of thousands of tons oil it supplies to North Korea annually.

On the issue of oil, one glimmer of hope to advocates for a change in Chinese behavior has been tied to an editorial in the Global Times, a Communist Party–backed publication, that threatened cutting oil shipments to North Korea. It certainly seems to signal impatience in Beijing, but Global Times is a particularly hawkish publication with tabloid tendencies — so it’s better to wait and see what Chinese leadership actually says.

So far, signs are not encouraging. During a meeting with reporters Wednesday, Chinese officials said that Beijing wasn’t willing to cut down on its overall trade with North Korea or even try to limit the sale of vehicles and other equipment that Pyongyang is directly using for military purposes.

“There are normal trading pacts between the two countries, and those trade relations actually touch upon the very livelihood of the regular people,” one of the officials told reporters.

He also painted the idea of maintaining trade with North Korea as a humanitarian obligation. “In the ancient Chinese philosophy, when you besieged a city, you have to leave one gate unbesieged — leave an opening so those who are besieged will not take the desperate actions,” the official said.

That rhetoric appears to accord with reality. China recently reported that its trade with North Korea has been expanding recently — trade between the countries grew more than 37 percent in the first quarter of 2017 compared with the same period the previous year.

The officials also said there were no plans to dismantle a jointly run Chinese-Korean industrial park, and that diplomatic efforts did not include any planned meetings with North Korean leader Kim Jong Un. On the whole, they sounded resolute that China’s relationship with North Korea would hew quite closely to the status quo.

China could yet be swayed. Kelly says that Trump’s unpredictable and unorthodox approach to diplomacy ultimately introduces a new variable into the mix.

“We’ve never had an American president threaten like this before,” he said. “Bush had ‘axis of evil,’ but he didn’t start openly calling out China publicly.”

Still, don’t expect China to do anything more than it feels it absolutely has to.