Embarking on a self-described "mission of peace," U.S. President Donald Trump's seat-of-the-pants foreign policy is facing its toughest test yet as he attempts this week to personally broker an end to North Korea's nuclear program in talks with Kim Jong Un.

In the historic first meeting between the leaders of the technically-still-warring nations, Trump is prioritizing instinct over planning.

Ever since Trump shocked allies, White House officials and, by some accounts, the North Koreans themselves, when he accepted Kim's March invitation for a meeting, the two leaders have lurched toward an uncertain encounter that could affect millions.

Trump landed in Singapore Sunday evening, about four hours after Kim arrived in the island city-state.

Moon's efforts to avert a potentially catastrophic U.S. first strike pushed Trump and Kim to take a risk.

The U.S. president said he will know "within the first minute" of meeting Kim whether the North Korean leader is serious about nuclear negotiations.

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