President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE reportedly worried that North Korea could pull the plug on a planned summit with the country's leader Kim Jong Un, and decided to cancel the meeting on Thursday before Kim got the chance.

NBC News reported that Trump's decision to nix the June 12 meeting with Kim in Singapore came shortly after the president and his top advisers began seriously discussing the prospect of withdrawing.

The decision was abrupt. Trump did not give a heads up to congressional leaders or key allies, NBC News reported. It was only after a series of phone calls between 7 a.m. and 9 a.m. on Thursday that Trump was sold on the decision to back out.

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The White House released Trump's letter to Kim announcing his decision at 9:42 a.m.

The New York Times reported over the weekend that Trump had privately pressed aides and allies about whether he should back out of the meeting, or risk possible political embarrassment if he went through with the summit.

But in the days that followed that report, officials in the U.S. and South Korea sought to downplay Trump's doubts.

On Tuesday, Chung Eui-yong, the national security adviser to South Korean President Moon Jae-in, said that Seoul believed there was a "99.9 percent chance" that the summit would materialize.

Secretary of State Mike Pompeo Michael (Mike) Richard PompeoOvernight Defense: Pentagon redirects pandemic funding to defense contractors | US planning for full Afghanistan withdrawal by May | Anti-Trump GOP group puts ads in military papers Overnight Defense: House Democrats unveil stopgap spending measure to GOP opposition | Bill includes .6B for new subs | Trump issues Iran sanctions after world shrugs at US action at UN Navalny calls on Russia to return clothes he was wearing when he fell ill MORE also said on Tuesday that the agency was continuing to make preparations for the meeting, despite recent threats by the North to back out.

But behind the scenes, officials were concerned about how serious the North was about the talks. A senior White House official said on Thursday that U.S. officials had been stood up by the North Koreans at a recent meeting.

"They waited and they waited," the official said. "The North Koreans never showed up. The North Koreans never told us anything. They simply stood us up."