U.S. President Donald Trump looks towards North Korean leader Kim Jong Un during the one-on-one bilateral meeting at the second North Korea-U.S. summit in Hanoi, Vietnam February 28, 2019. REUTERS/Leah Millis

U.S. President Donald Trump meets North Korean leader Kim Jong Un during the one-on-one bilateral meeting at the second North Korea-U.S. summit in Hanoi, Vietnam February 28, 2019. REUTERS/Leah Millis

North Korean leader Kim Jong Un speaks during the one-on-one bilateral meeting with U.S. President Donald Trump at the second North Korea-U.S. summit in the Metropole hotel in Hanoi, Vietnam February 28, 2019. REUTERS/Leah Millis

North Korea's leader Kim Jong Un and U.S. President Donald Trump talk in the garden of the Metropole hotel during the second North Korea-U.S. summit in Hanoi, Vietnam February 28, 2019. REUTERS/Leah Millis

North Korean leader Kim Jong Un and U.S. President Donald Trump walk in the garden of the Metropole hotel during the second North Korea-U.S. summit in Hanoi, Vietnam February 28, 2019. REUTERS/Leah Millis

U.S. President Donald Trump and North Korea's leader Kim Jong Un walk in the garden at the Metropole hotel during the second North Korea-U.S. summit in Hanoi, Vietnam February 28, 2019. REUTERS/Leah Millis

Kim Yo Jong, sister of North Korea's leader Kim Jong Un and first vice department director of the ruling Workers Partys Central Committee, looks on in the garden of the Metropole hotel during the second North Korea-U.S. summit in Hanoi, Vietnam February 28, 2019. REUTERS/Leah Millis

North Korea's leader Kim Jong Un, U.S. President Donald Trump, Kim Yong Chol, Vice Chairman of the North Korean Workers' Party Committee, and U.S. Secretary of State Mike Pompeo talk while Kim Yo Jong, sister of North Korea's leader Kim Jong Un and first vice department director of the ruling Workers Partys Central Committee looks on at the Metropole hotel during the second North Korea-U.S. summit in Hanoi, Vietnam February 28, 2019. REUTERS/Leah Millis

North Korea's leader Kim Jong Un and U.S. President Donald Trump attend the extended bilateral meeting in the Metropole hotel with U.S. Secretary of State Mike Pompeo, White House national security adviser John Bolton, acting White House Chief of Staff Mick Mulvaney, North Korean Foreign Minister Ri Yong Ho and Kim Yong Chol, Vice Chairman of the North Korean Workers' Party Committee, during the second North Korea-U.S. summit in Hanoi, Vietnam February 28, 2019. REUTERS/Leah Millis

North Korea's leader Kim Jong Un sits alongside Kim Yong Chol, Vice Chairman of the North Korean Workers' Party Committee, and North Korean Foreign Minister Ri Yong Ho at the extended bilateral meeting with U.S. President Donald Trump (not pictured) in the Metropole hotel during the second North Korea-U.S. summit in Hanoi, Vietnam February 28, 2019. REUTERS/Leah Millis

White House national security adviser John Bolton reacts beside U.S. President Donald Trump and Secretary of State Mike Pompeo at the extended bilateral meeting in the Metropole hotel with North Korea's leader Kim Jong Un (not pictured) during the second North Korea-U.S. summit in Hanoi, Vietnam February 28, 2019. REUTERS/Leah Millis

A view of the table in the room which was supposed to host a working lunch between U.S. President Donald Trump and North Korean leader Kim Jong Un, that was cancelled, during the second U.S.-North Korea summit at the Metropole Hotel in Hanoi, Vietnam, February 28, 2019. REUTERS/Leah Millis -

North Korean journalists wait for North Korean leader Kim Jong Un at Dong Dang railway station in Vietnam, March 2, 2019. REUTERS/Kim Kyung-Hoon

Women wave North Korean and Vietnamese flags as the motorcade transporting North Korean leader Kim Jong Un arrives at Dong Dang railway station, where his train will depart at the border with China, in Dong Dang, Vietnam March 2, 2019. REUTERS/Kim Kyung-Hoon

North Korean leader Kim Jong Un bids farewell to the crowd before boarding his train to depart for North Korea at Dong Dang railway station in Vietnam March 2, 2019. REUTERS/Kim Kyung-Hoon

North Korean leader Kim Jong Un bids farewell before boarding his train to depart for North Korea at Dong Dang railway station in Vietnam March 2, 2019. REUTERS/Kim Kyung-Hoon