“The most important principle we have identified,” said Chinese Foreign Minister Wang Yi on Saturday referring to North Korea, “is that no matter what happens, we have to stay committed to diplomatic means as a way to seek a peaceful settlement.”

Do we? Washington over the course of decades has been seeking peaceful settlements with Pyongyang, talking, negotiating, and conversing directly and indirectly in every conceivable format, formal and informal, bilateral and multilateral. Discussions have been held at the United Nations, in the capitals of the participants, and in neutral venues around the world.

Yet every agreement with the Kims has fallen apart for one reason or another, sometime from misunderstanding but more often due to the regime’s duplicity. Nothing has worked, at least for America.

Secretary of State Rex Tillerson, who met with Minister Wang, is losing patience, even though he has been on the job for only six weeks. As he refreshingly said on Thursday during his visit to Tokyo, “The diplomatic and other efforts of the past 20 years to bring North Korea to a point of denuclearization have failed.”

Make that 30 years, and the statement is even more correct. Washington has been negotiating with the Kim family, in one way or another, since the 1980s.

There have been moments when success appeared close at hand. Three of them—one each from the Clinton, Bush, and Obama administrations—are notable. First, the Clinton administration signed the Agreed Framework, a grand-bargain-type deal, in Geneva in October 1994.

Pursuant to this arrangement—Clinton officials did not call it a treaty to avoid the necessity of Senate ratification—North Korea froze its nuclear reactor in Yongbyon and “related facilities” in return for proliferation-proof light-water reactors. Pyongyang agreed to remain a part of the Nuclear Nonproliferation Treaty, the global pact, and accept international monitoring. Moreover, both sides agreed to reduce barriers to trade and investment, open liaison offices in each other’s capital, “move toward full normalization of political and economic relations,” and commit to reaching a deal on the “peaceful uses of nuclear energy.”

Second, there was an arrangement dubbed “Framework Two,” a statement of principles that, in broad outline, resembled the 1994 agreement in that both contemplated the supply of light-water reactors to the North for electricity-generation purposes. This September 2005 bargain, a product of the now-dormant Six-Party Talks, also contained Pyongyang’s commitment to disarm and promises of across-the-board cooperation.

Third, the Obama administration negotiated the Leap Day Deal, another unsigned arrangement, in February 2012. In a pair of brief statements, which were not identical, Washington and Pyongyang made various promises, the most important of which was a moratorium on North Korean missile launches and nuclear tests.

None of these deals lasted long. The 1994 Agreed Framework eventually collapsed for various reasons, mostly because the North Koreans, while agreeing to freeze their plutonium facilities at the Yongbyon site, were secretly enriching uranium to weapons-grade at other locations.

Framework Two fell apart quickly because there was no real agreement, something highlighted by the differing interpretations issued by all six parties to the arrangement. Moreover, North Korea was never really committed to the deal. The day after the announcement of Framework Two, Pyongyang publicly demanded reactors before turning over its weapons, a schedule not within the contemplation of the five other parties. On the day after that, the North’s Korean Central News Agency threatened nuclear war with America.

And the Leap Day Deal? Sixteen days after the exchange of statements constituting the arrangement, which included the moratorium on missile launches, Pyongyang announced plans to send a satellite into orbit, scuttling the entire agreement.

These three agreements, spanning three decades and three American administrations, all failed. If there is a common denominator, it is that none of the three Kims involved—Kim Il Sung, Kim Jong Il, and current ruler Kim Jong Un—could deal in good faith.

Today the regime appears to be even more insecure than usual. Since late January, the minister of state security was demoted; five of his senior subordinates were executed by antiaircraft fire; the elder half-brother of Kim Jong Un was assassinated with VX, a chemical nerve agent; and the general in charge of the country’s missile forces was absent from the Feb. 12 launch of the intermediate-range missile, indicating turmoil at the top of the North Korean military.

The Chinese foreign minister may think negotiation with Pyongyang is a good idea, but it’s not clear there is anybody for America to negotiate with. As Tillerson said on Friday, “We do not believe the conditions are right to engage in any talks at this time.”

Over the last three decades, there may have been only one moment when a deal with North Korea was remotely possible. That was in the second term of the Bush administration, when the Treasury Department in 2005 froze $25 million belonging to the North and cut off its links to the global financial system by designating a front bank in Macau a “primary money laundering concern” under the Patriot Act.

Then, a shaken Kim Jong Il—he needed the locked-up cash for his “gift politics,” the buying of regime elements with luxury goods—looked like it might be willing to come to some accommodation on its weapons programs in order to reconnect lifelines to the global banking system. Unfortunately, the Bush White House, at China’s incessant urging, unfroze North Korea’s funds in 2007.

Pyongyang, predictably, pocketed the concession and promptly walked away from the Six-Party Talks. As The Wall Street Journal stated in an editorial Friday, “Bush-era diplomats Condoleezza Rice and Christopher Hill have a lot to answer for after they persuaded President Bush to give up a pressure campaign against the North that was showing signs of success.”

And that is one lesson Washington should remember: Never let up pressure on North Korea until it completely and irrevocably disarms. Today, many say the U.S. is “sanctioned out,” in other words, that there is no more pressure that it can apply to an already isolated Kim regime. That’s not true for two reasons.

First, the current sanctions regime on North Korea is not as strict as the U.S. has maintained on other bad actors.

Second, Washington can pressure China to pressure North Korea. What leverage does the Trump administration possess on the so-called owner of the 21st century? Washington can sanction Chinese banks, especially Bank of China, that have participated in the North’s illicit commerce.

And now is the best time to threaten this. The Chinese economy is fragile, not growing at the claimed 6.7 percent pace and facing a debt crisis, and it may only take the threat against Chinese banks to move Beijing to cooperate.

Trump’s Treasury Department would rock global markets if it unplugged Chinese financial institutions from their dollar accounts in New York, but it would show Beijing for the first time since 1994 that Washington was serious about protecting the American homeland. It is hard to convince Chinese leaders to act when U.S. presidents have not made North Korea their first priority. Moreover, that bold move would have the added benefit of crippling Pyongyang’s sanctions-busting network of front companies and agents.

China, which accounts for more than 90 percent of the North’s foreign trade, still has the ability to push Pyongyang in better directions. Beijing might not be able to change Kim Jong Un’s mind, but it can, by starving regime elements of cash, convince them that their support of the Kimster’s weapons programs is not in their long-term interests.

Imposing severe costs on China to get it to influence North Korea is the only tactic Washington has not tried over the course of decades. It may not succeed in jumpstarting negotiations, but all the other policy approaches are virtually guaranteed to fail.

“The threat of North Korea is imminent,” Tillerson told the Independent Journal Review last week as he traveled to Beijing from Seoul. He’s right, and it’s about time Washington acts like it in fact is.