FOR many years, a plausible case could be made that two forms of timidity, one Chinese and one American, were blocking the sort of strategy that might—just might—make North Korea suspend or abandon its sprint to a nuclear arsenal. Start with the Chinese.

In theory, the prospect of a nuclear-armed North Korea peninsula worried Communist leaders in Beijing every bit as much as it did the Americans. The problem was that in China’s hierarchy of horrors, a nuclear-armed Korean dictator ranked very high, but just below the prospect of regime collapse in North Korea. That surpassing Chinese horror of instability meant that, to simplify, China’s rulers were willing to agree to any level of sanctions on North Korea, except those horrible enough to stand a chance of success.

The Americans stand charged with their own form of timidity. Since George H.W. Bush, successive presidents have steeled themselves to negotiate with North Korea about its nuclear and missile programmes. America has offered massive bribes in return for freezes that were undermined by cheating each time. American presidents have offered painful concessions, including the withdrawal of all sea- and land-based tactical nuclear weapons deployed abroad in 1991, a step that was necessary to get the North Koreans to the table for talks starting in 1993.

But after years and years of haggling between official and semi-official envoys, it has become clear that the concessions sought by North Korea go too far. To simplify, the hereditary Stalinist regime of the Kim dynasty wants America to break its formal defence alliances with Japan and South Korea, and to remove all military assets from South Korea. Because that is deemed a price too high to pay, it could be said that America has been willing to consider any negotiating position, short of one that might actually work.

Now the time for timidity is ending. North Korea has shocked the world by testing intercontinental ballistic missiles that may be capable of hitting the West Coast of America. This week, on the sidelines of the UN General Assembly in New York, the regime’s foreign minister, Ri Yong-ho, said that his country might be considering a test of a hydrogen bomb over the Pacific Ocean. President Donald Trump called Kim Jong-un, the young dictator of North Korea, a “Rocket Man” bent on a “suicide mission”. Mr Kim responded with an unusual personal statement, calling Mr Trump a “mentally deranged US dotard”, who had convinced him that his course of seeking nukes is “correct” and needs to be followed “to the last”.

In this alarming moment, the Chinese this week agreed to some of the most sweeping sanctions yet. China’s central bank instructed the country’s banks not to agree new loans with North Korea and to wind down existing finance deals. Mr Trump unveiled an executive order imposing the most aggressive American sanctions on North Korea to date, including financial sanctions liable to have a chilling effect on the large Chinese banks that operate in America. Under Mr Trump’s order, international banks that facilitate transactions with North Korean entities risk being banned from the American market—an effective death sentence for a global bank. Behind the scenes, Washington, DC is rife with talk of Treasury officials threatening Chinese banks with hefty fines for aiding and abetting deals involving North Korea, even at arm’s length.

In private, Chinese and American officials have rarely sounded so similar in their scorn and anger for North Korea. True, the Americans still accuse the Chinese of selfishly failing to enforce the harshest and most crippling sanctions. Some hawks in Washington growl that the Chinese secretly like the way that North Korea keeps the Americans bogged down, and too distracted to challenge bad behaviour by Chinese naval forces and paramilitaries in the South China Sea.

For their part the Chinese accuse the Americans of a selfish lack of imagination, for failing to offer such concessions as a freeze on large-scale military exercises with their allies in South Korea. Nationalists in Beijing growl that the Americans are using exaggerated fears of North Korea to encircle and contain China. But still the Chinese have some reasons to hope for a breakthrough. Mr Trump says that dialogue with North Korea is still possible—“why not?” he told a reporter in New York this week. He is if nothing else an unconventional deal-maker with a taste for surprises.

Broadly, then, the two countries are in unprecedented agreement over North Korea. Alas, it may be too late. Kim Jong-un is painfully close to developing his great ambition, the nuclear-tipped missiles capable of hitting American territory that he sees as an insurance policy against attack, and as his ticket to being treated as a near-equal by America. In particular, senior officials and ex-officials on both sides see no reason why he will stop now. They privately call sanctions deserved and necessary, but insufficient. The problem is that any embargo brutal enough to have a chance of bringing the Kim regime to its knees would risk a humanitarian catastrophe, including mass starvation. Even that might not be enough. In 1990s North Korea’s Stalinist, quasi-feudal rulers rode out a mass famine without falling.

Nikki Haley, the American ambassador to the United Nations, conceded publicly this week to the New York Times that tougher sanctions might fail: We always knew that the sanctions may not work,” she said. “What the goal of the sanctions was always intended to be is to cut the revenue so that they could do less of their reckless behaviour.”

Listen to insiders in Washington, and it is easy to wonder if this will one day be seen as a high point of Chinese-American agreement. For if and when North Korea unveils a full-scale nuclear arsenal, America will be left with no choice but to pursue Cold War style policies of deterrence and containment. Experienced folk worry that China will hate a lot of what America has to do at that point, to contain a nuclear North Korea. America might have to deploy tactical nuclear weapons once more. More anti-missile THAAD systems may need to be installed in South Korea, bringing powerful radar systems that can see deep into China. American missile defence batteries will need beefing up in such places as Fort Greeley, Alaska, in such a way that China may feel its “second strike capability”, or ability to retaliate after a nuclear attack, is jeopardised.

It is hard to see much that is cheering about these days of confrontation and nuclear-armed bluster. But if the Asia-Pacific is plunged into a new Cold War, this moment of Chinese-American agreement will be missed.