The air of uncertainty was confirmed by Trump himself.
"I believe we're going to have a terrific success or a modified success", Trump said during a press conference last week with Japanese Prime Minister Shinzo Abe.
He also shared a photo of himself and Trump and told the entire world that he's "honored" to call the president a friend.
Trump and Kim arrived in Singapore hours apart Sunday.
Trump's early exit will be his second from a summit in just a few days. Trump traveled to Singapore from Canada, where he a meeting with other world leaders.
A jet carrying Kim landed hours earlier. As the site for their meeting, the two leaders have chosen one of Singapore's most luxurious hotels, the Capella Resort on Sentosa Island, a popular vacation spot off the southern tip of Singapore and home to Universal Studios Singapore.
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He said that the cost is all part of the $20 million Singapore is spending to host the meeting.
AFP 2018 Saul Loeb World Follows Every Step of Historic Trump Kim Summit
Trump spoke only briefly in public on Monday, forecasting a "nice" outcome.
The MFA also said Lee will meet President Trump separately on Monday. The talks are expected to be devoted to the future of Pyongyang's nuclear program and the lifting of economic sanctions.
It was a striking about-face from less than a year ago, when Trump was threatening "fire and fury" against Kim, who in turn scorned the American president as a "mentally deranged USA dotard".
White House press secretary Sarah Huckabee Sanders said Sung Kim, the U.S. ambassador to the Philippines who has taken the lead on policy negotiations with the North, will hold a "working group" with a North Korean delegation to discuss final preparations for the meeting. Add North Korea as an interest to stay up to date on the latest North Korea news, video, and analysis from ABC News.
But it was only Monday morning in North Korea that the government news agency reported that Kim was in Singapore, had met with Prime Minister Lee Hsien Loong and would meet Trump on Tuesday. But no one can credibly suggest that a durable or verifiable denuclearization of the Korean peninsula can be achieved when North Korea remains a completely closed and totalitarian state.
Trump initially touted the potential for a grand bargain with North Korea to rid itself of a nuclear missile program that has advanced rapidly to threaten the United States. Pyongyang has advocated for decades for a peace treaty to formally end the Korean War, rather than the armistice that has been in place for more than 60 years. North Korea also wants an end to what it considers America's "hostile policy" and a security guarantee that the USA will not seek to remove the regime.
First lady attends annual Ford's Theatre gala in Washington
The source added: "I don't know exactly when the move is supposed to happen, but it is being talked about as a permanent move". She delivered remarks at the end of performances, thanking the theater and performers, according to the first lady's office.