Transcript for Trump sets off for Vietnam with high hopes for second summit

tonight, president trump is in the air at this hour, on his way to Hanoi, where he will meet for the second time with north Korean dictator Kim Jong-un. The president predicting a, quote, very tremendous summit. His secretary of state over the weekend now contradicting that. Kim Jong-un seen boarding his armored train in Pyongyang, traveling through China, on his way to Vietnam. But back in the U.S., much of this will be on a split careen of sorts, as the president's long-time fixer and personal attorney general, Michael Cohen, answers questions in front of the American people, as the summit plays out, as well. ABC's chief white house correspondent Jonathan Karl from Hanoi tonight. Reporter: The president took off for Hanoi today eager to leave his political problems behind and hungry for a win on the world stage. I think we'll have a very tremendous summit. We want denuclearization. Reporter: The president believes he can succeed where his predecessors failed. But he faces skeptics, some in his own administration, who say Kim Jong-un has no untension of giving up his nuclear weapons. After their historic summit in Singapore, president trump declared, "There is no longer a nuclear threat from north Korea." Just this weekend, his own secretary of state said the opposite. We're very hopeful we can get a good outcome. Do you think North Korea remains a nuclear threat? Yes. Reporter: There's evidence North Korea has continued to make fuel for its bombs. And now the president is lowering expectations. I'm not in a rush, I don't want to rush anybody. I just don't want testing. As long as there is no testing, I'm happy. Reporter: North Korea has conducted no nuclear tests or major missile tests since the Singapore summit, something president trump attributes to the relationship he has forged with Kim Jong-un. I have a very, very good relationship with Kim Jong-un, very, very good. We went back and forth, and then we fell in love, okay? No, really. He wrote me beautiful letters. Reporter: The north Korean dictator is looking for a win, too, eager to free his country from crippling economic sanctions. He set off on a two-day journey to Vietnam with great fanfare on an armored train. North Korea's state-owned aircraft are believed to be too old and battered to make the journey. For the last summit, Kim borrowed an airplane from China. This time, he chose to make the nearly 3,000-mile journey by land. Jon Karl with us live tonight from Hanoi. And Jon, with the president in the air, he knows and so does this white house tonight that many will be watching this summit play out, as they watch Michael Cohen testify before congress. Reporter: In fact, David, Michael Cohen was on capitol hill today preparing for that testimony. He's going to be asked about those hush money payments during the campaign, about trump tower Moscow and many other things. And, of course, Cohen already faces jail time for lying to congress, but now, he says, he is ready to tell the truth, as he tweeted last week, "Looking forward to the American people hearing my story in my voice." It will be quite the split screen moment, David.

This transcript has been automatically generated and may not be 100% accurate.