WASHINGTON – US President Donald Trump canceled what was meant to be a landmark peace summit with North Korean dictator Kim Jong-un in Singapore next month, and on Thursday returned to a posture that last year brought their two nations to the brink of nuclear-armed conflict.

The White House Communications Agency had already printed coins commemorating the event, and the US Secret Service was on the ground organizing security throughout Singaporean hotels. But Trump administration officials began to fear the president might arrive at the island nation only to be a bride left at the altar, as North Korean officials began to shift the tone of their rhetoric in recent days, suggesting their leader might not show.

Testifying before a Senate panel, Mike Pompeo, Trump’s new secretary of state, said the US negotiating team “got a lot of dial tones” in the past 24 hours when trying to call the North Koreans for summit preparations. And overnight, as the North Korean military blew up one of its nuclear test sites before Western cameras in a gesture of goodwill to the US ahead of the meeting, a vice minister in North Korea’s Foreign Ministry called Vice President Mike Pence a “political dummy” and warned of a nuclear “showdown” with Washington. Their threat was familiar North Korean rhetoric, but a break from the restraint Pyongyang had recently shown in the lead-up to Kim’s scheduled meeting with Trump.

Trump administration officials were also spooked when, earlier this month, North Korean officials abruptly canceled talks with their South Korean counterparts, citing their participation in military drills with the US that Kim previously said he understood had to take place.

On Thursday, Trump said he had spoken with Defense Secretary James Mattis and Chairman of the Joint Chiefs of Staff Joseph Dunford to ensure the US military was “ready if necessary” should Pyongyang respond to the cancellation with provocations.

“Likewise, I have spoken to South Korea and Japan,” Trump told the press after releasing his formal letter addressed to Kim. “They are not only ready should foolish or reckless acts be taken by North Korea, but they are willing to shoulder much of the cost of any financial burden – any of the costs associated – by the United States in operations if such an unfortunate situation is forced upon us.”

“Hopefully, positive things will be taking place with respect to the future of North Korea,” he continued. “But if they don’t, we are more ready than we have ever been before.”

In the letter, Trump wrote that Pyongyang’s “tremendous anger and open hostility” made the upcoming summit “inappropriate.” He unsubtly referenced the size and power of America’s nuclear-weapons arsenal and said he hoped never to employ it.

“I felt a wonderful dialogue was building up between you and me, and ultimately, it is only that dialogue that matters,” Trump wrote. “If you change your mind having to do with this most important summit, please do not hesitate to call me or write.”