Within hours of North Korea's nuclear test on Friday, the United States began its latest push for new sanctions against the isolated country; President Obama even threatened unilateral measures to curb its nuclear ambitions.
But without the help of China, a declaration by a North Korean foreign ministry official on Sunday that the threat of further sanctions was "laughable" may prove truer than many American officials care to admit.
Such cooperation seems remote. China has long provided diplomatic cover to Pyongyang, and though the latest nuclear test has surely tested Beijing's patience, analysts say it's more unlikely than ever to tighten the economic screws on its neighbor, despite its increasing belligerence.
"China balances two things: stability and denuclearization," says David Kang, a professor of international relations at the University of Southern California. "No one really expects China to deeply implement sanctions unless it's in their own interest."
Beijing's interest now, says Prof. Kang, is to maintain the status quo. That's because the alternative could be a failed North Korean state, millions of refugees pouring into China, and a reunified Korean peninsula within Washington's orbit.
China remains Pyongyang's only political ally and economic lifeline, providing it with enough oil to keep its economy alive. North Korea's position as a buffer between China and South Korea, a US treaty ally, means that even its illegal nuclear program does not put its ties with Beijing at risk.
China's readiness to pressure its ally, never robust, has waned further in recent months, says Stephan Haggard, director of the Korea-Pacific program at the University of California, San Diego. US plans to deploy an advanced missile defense system in South Korea are seen in Beijing as a threat to its own security. Mr. Obama's insistence on installing the Terminal High Altitude Area Defense system, or Thaad, has fed China's reluctance to clamp down on Pyongyang.
"The Thaad decision was just a gold mine for North Korea," says Prof. Haggard. "It has driven a wedge between China and the US."
Meanwhile, pressure from the US on China to rein in its rogue neighbor continues to mount. US Defense Secretary Ash Carter said China "shares important responsibility" for the latest nuclear test, North Korea's second in eight months and its largest one to date.
"It's China's responsibility," Mr. Carter said Saturday at a press conference during an official visit to Norway. "It's important that it use its location, its history, and its influence to further the denuclearization of the Korean Peninsula."
So far Beijing has shown no sign of altering its strategy. On Friday, the Chinese government and state-run media issued their usual statements of condemnation. The Xinhua News Agency said in an editorial that the nuclear test had "shocked the world" and was in violation of UN Security Council resolutions.
"All parties including North Korea should recognize that tumult on the peninsula, war and instability in Northeast Asia will benefit nobody," the editorial said, adding that South Korea's deal with the US on Thaad had contributed to a rise in regional tensions.
In March, China signed on to the toughest sanctions ever imposed by the United Nations Security Council against North Korea after its fourth nuclear test in January and a long-range rocket launch in February. The sanctions banned North Korea from exporting coal, a major source of income for the regime, and from importing jet fuel.
Yet a study published last month by researchers at Harvard University and MIT concluded that North Korea has successfully evaded many sanctions by trading through branches of state-run companies it has opened in China. The researchers, John Park and Jim Walsh, found that sanctions have actually improved the North's ability to procure components for its nuclear and missile programs from China and other countries.
"China is far and away the most important player in North Korean trade and procurement," the report says. "No sanctions regime targeting North Korea will be successful without robust participation by Beijing."
Taking the gloves off
Haggard says trade between China and North Korea continues in the North's shadowy business dealings across the border and by exploiting loopholes in the UN sanctions. This has fueled growing impatience in Washington and led to renewed calls for unilateral action.
"There's lot of pressure from Congress to take the gloves off," Haggard says.
One possibility is that the US might ban banks that do business with North Korea – many of which are Chinese – from dealing in dollars. But Zhao Tong, a nuclear policy researcher at the Carnegie-Tsinghua Center for Global Policy in Beijing, warns that such a move would enrage China and dissuade it from further cooperation with the US.
Mr. Zhao says China could decide to increase its pressure by more strictly enforcing the sanctions on North Korean coal and other minerals to which it agreed last March. But it is unlikely to go further.
"The next big step in terms of international sanctions is to call on every country to cut off all trade and economic ties with North Korea," Zhao says. "That is a red line Beijing is unwilling to cross."
A more realistic way forward, he suggests, is for the US to pursue multilateral negotiations that could lead to a short-term freeze of North Korea's nuclear program rather than full-scale denuclearization. For now, Washington appears unwilling to compromise on that point.
"Our hope is that ultimately we can get back to the talks. We're prepared to go back right away," Secretary of State John Kerry said in Geneva on Saturday. "All Kim Jong-un has to do is say, 'I'm prepared to talk about denuclearization.' "