In a region where the subtlest of signals sends shockwaves, this one looks like a tsunami. Talks between the US and South Korea broke down earlier today in a remarkable show of public acrimony, with the Trump administration’s negotiator accusing Seoul of acting in bad faith. At issue is the bill that the White House wants South Korea to pay for our military protection, which quintuples Seoul’s current contribution:

The United States broke off talks with South Korea on Tuesday over how to share the cost of the two nations’ military alliance, injecting fresh tension into the relationship over Washington’s demands that Seoul pay sharply more.

President Trump has demanded South Korea raise fivefold its contribution to cover the cost of stationing 28,500 U.S. troops in the country, asking for nearly $5 billion, officials on both sides said. But that demand has triggered anger from Korean lawmakers and sparked concerns that Trump may decide to reduce the U.S. troop presence in the Korean Peninsula if talks break down.

The top U.S. negotiator, James DeHart, said the U.S. side decided to cut short the negotiations on Tuesday morning, the second of two days of planned talks. In a rare public show of disunity between the allies, he blamed South Korea for making proposals that “were not responsive to our request for fair and equitable burden sharing.”

“As a result we cut short our participation in the talks today in order to give the Korea side time to reconsider,” he said in a statement. “We look forward to resuming our negotiations when the Korean side is ready to work on the basis of partnership, on the basis of mutual trust.”

Trump has slammed NATO allies over their lack of proper contribution to common defense resources, so this isn’t out of the blue. The administration has raised the issue with South Korea before too, but until now managed to keep the issue from looking as though it had become a point of fracture. To do otherwise would be to send a very bad signal to North Korea that they can peel the US away from Seoul and start using their nuclear arms to pressure the South into capitulation — a situation that would present dire concerns to Japan.

So why allow this to blow up so spectacularly in public now? Trump might be getting tired of having his funding demands left unmet, part of his usual hardball negotiating tactics. Perhaps it also has something to do with signals out of Pyongyang the day before:

President Trump hinted at a possible meeting with North Korean leader Kim Jong Un on Sunday, tweeting to the leader he addressed as “Mr. Chairman” that he would “see you soon!” But hours later, North Korean state media responded with a curt message: We don’t want a meeting if we don’t get anything from it.

In a statement to the Korean language website of the official Korean Central News Agency on Monday, Foreign Ministry adviser Kim Kye Gwan said that he had read Trump’s Twitter post but that North Korea was not interested in another fruitless meeting. …

Despite three meetings between Trump and Kim, “there has not been much improvement in relations with the United States,” wrote Kim Kye Gwan, a veteran diplomat who previously led the North Korean delegation in six-party denuclearization talks.

“We are no longer interested in such talks that bring nothing to us,” the statement continued. “As we have got nothing in return, we will no longer gift the U.S. president with something he can brag about, but get compensation for the successes that President Trump is proud of as his administrative achievements.”

That puts the shoe on the other foot. One of the criticisms of Trump’s attempt at personal negotiation with Kim had been that it unnecessarily raised the dictator’s profile as a legitimate head of state and a credible statesman. The insult intended by reversing that criticism and applying it to Trump cannot possibly have been missed. They are also openly accusing Trump of “betrayal” by not offering more incentives for bilateral progress.

At the very least, this leaves an apparent vacuum on the Korean peninsula. And guess who’s swooping in to fill it? This development didn’t get much attention yesterday, but after today’s diplomatic rupture, it should:

The defence ministers of South Korea and China have agreed to develop their security ties to ensure stability in north-east Asia, the latest indication that Washington’s long-standing alliances in the region are fraying.

On the sidelines of regional security talks in Bangkok on Sunday, Jeong Kyeong-doo, the South Korean minister of defence, and his Chinese counterpart, Wei Fenghe, agreed to set up more military hotlines and to push ahead with a visit by Mr Jeong to China next year to “foster bilateral exchanges and cooperation in defence”, South Korea’s defence ministry said.

Seoul’s announcement coincided with growing resentment at the $5 billion (£3.9bn) annual fee that Washington is demanding to keep 28,500 US troops in South Korea.

China would love nothing more than to squeeze the US off the Korean peninsula and make both regimes reliant on Beijing. It would greatly enhance its prestige, force the US out of a strategic position in Asia, and send a signal to Japan that it should rethink its own partnerships in light of American vacillation and self-interest. Thus far, it looks as though China won’t even need to offer trade concessions to the US in that exchange — they’ll just develop it on their own as the US infuriates Seoul.

This is a disaster in the making of far more importance than anything relating to Ukraine. Perhaps Trump has some master plan in place, but so far it hasn’t paid off in anything except North Korea’s occasional moratoriums on weapons testing and some photo ops. If Trump loses South Korea to China over $4 billion, it’s not going to look like greatness to anyone.