Trump reacted by criticizing his predecessors for allowing this perceived threat to develop; aiming tough (and at times insulting) talk at North Korea's young leader, Kim Jong Un, while also expressing a willingness to meet with him directly; and organizing a successful push for United Nations-backed sanctions created to bring North Korea either to the negotiating table or to its knees.
However it would not be surprising for Beijing to allow increased informal trade with Pyongyang, given Kim's improved relationship with Xi, and the unilateral good faith measures taken by the North that include the destruction of it nuclear test site on Thursday, the release of US prisoners, and the continued suspension of further nuclear and missile tests.
The move may have shocked the world but as the BBC's Heather Chen and Minji Lee of BBC News Korean write, it's an even bigger setback for the people at the heart of it: North and South Koreans.
Kim Kye Gwan's statement is the latest whiplash development in efforts to diplomatically address what might be the world's most unsafe standoff.
But there was lingering concern among US officials that Kim was not serious about relinquishing the nuclear weapons his country has developed for decades - an issue that will continue to complicate any future talks.
The stakes are high.
"It won't be like a year ago when South Korea and the USA stressed their firm alliance and pressured North Korea", he told AFP.
Analysts have decried the pace of events over the last few months, pointing out that the diplomatically untested businessman-president appeared to have little understanding of the complexities of dealing with North Korea. The Singapore summit would have been the culmination of this outreach.
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May 25: North Korea says it's still willing to sit for talks with the United States "at any time, (in) any format". Moon urged direct talks between Trump and Kim to get things back on track.
North Korea's vice foreign minister expressed sadness the meeting had been called off, but praised Trump for making a bold decision to hold the summit and said the North was open to meeting at any time.
Only a day before the sudden U-turn, Trump and USA officials had been indicating there was every chance the historic pow-wow between a sitting American president and the third generation Kim would go ahead in Singapore. "His sudden and unilateral announcement to cancel the summit is something unexpected to us and we can not but feel great regret for it".
"It is meaningless to hold a summit if it does not bring about progress", he said, adding that Japan still thinks Washington and Pyongyang should meet in the future.
Trump then issued his own threat in a letter to Kim. But his position is a bit more complicated. Obama or (Bill) Clinton could have accepted (these kinds of North Korean statements).
"China is likely to more openly back North Korea". In the meantime, I want to thank you for the release of the hostages who are now home with their families.
"It looks like we are back to fire and fury as the modus operandi for the White House again after President Trump (threatened) a new 25 percent auto import tariff and cancelled the summit with North Korea", said Greg McKenna, chief market strategist at AxiTrader. "Not only was it going to be a nightmare in terms of traffic, but Trump would have gotten credit for the summit when it was just the result of being in the right place at the right time". Trump attributed this to the changing behaviour of Kim and North Korea.
In a separate statement at the White House, Mr Trump said the step was a "tremendous setback for North Korea and the world", adding the U.S. military was "ready if necessary" to respond to any "reckless" act from North Korea.