South Korea's president, Moon Jae-in, helped broker the planned meeting between Kim and Trump.
"Therefore, please let this letter serve to represent that the Singapore summit, for the good of both parties, but to the detriment of the world, will not take place", the letter read. This missed opportunity is a truly sad moment in history.
Another factor was the North Koreans' silence over the past five to 10 days, Brennan reports. Further complicating matters, advisors within the White House seemed split on how to handle Kim, and the U.S. president insists in general on ignoring diplomatic experts.
To his credit, Mr. Trump has accepted the urgency of solving the North Korean threat.
The decision to scuttle the summit came after a late-night huddle between Pompeo, Bolton, the vice president and the president, following a North Korean statement slamming Pence.
Trump also appeared to make an apparent threat about the U.S.'s nuclear stockpile, writing: "You talk about you nuclear capabilities, but ours are so massive and powerful that I pray to God they will never have to used".
He said in the letter that the world is losing a "great opportunity for lasting peace and great prosperity and wealth" now that the summit has been cancelled.
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That the USA has now abruptly pulled out of the summit is likely to be seen as a massive breach of trust despite Mr Trump's emollient language in his letter.
Meanwhile, the senior White House official defended Trump's decision and said it was due to a "trail of broken promises" from North Korea that Trump chose to scrap the meeting.
Trump opponents said he botched a delicate, diplomatic dance with North Korea, at the risk of fueling tensions, cold-shouldering allies like South Korea and making China less willing to put economic pressure on Pyongyang. And "Kim Jong Un wants to do what's right", adding, "I really believe that".
April 31-May 1: Then-CIA Director and soon-to-be Secretary of State Mike Pompeo made a secret trip to North Korea over Easter. The president has openly entertained the idea that he could have been awarded the Nobel Peace Prize had the meeting led to a peace agreement between North Korea, the US and South Korea.
Mr Pompeo said he did not think the summit's cancellation was a sign that Mr Kim is a "weak leader".
We will neither beg the United States for dialogue nor take the trouble to persuade them if they do not want to sit together with us.
"We've not been able to conduct the preparations between our two teams that would be necessary to have a successful summit".
The cancellation will be a major personal blow to South Korean president Moon Jae-in, who has played a key role in the thawing of relations between Washington and Pyongyang in recent months, which began in earnest with the attendance of a North Korean delegation at the Winter Olympics in February in South Korea.
"There has been a trail of broken promises that gave the United States pause", a White House official told reporters, according to South Korean media outlet Yonhap News.
Looks like President Trump just called Kim Jong-un's bluff.