Transcript for Trump and Kim Jong Un fail to reach agreement during summit

from Hanoi, where we witnessed the abrupt collapse of talks today between president trump and north Korean dictator Kim Jong-un. President trump saying sometimes you have to walk. Tonight, his critics asking, why did he put Kim Jong-un back on the world stage, allowing him to sit across from an American president without know what was going to happen? Before it all fell apart, there was the dinner last night, then the meeting today. The north Korean dictator even took a question from a reporter on denuclearization, something he's never done before. But a short time later, the announcement. The working lunch was canceled. The table empty. The white house revealing no agreement. And tonight, the north Koreans, just a short time ago, taking on the president with their own version of what happened here. ABC's chief white house correspondent Jonathan Karl here in Hanoi. Reporter: Just hours after the two leaders sat down, the high stakes summit took a dark turn. With the table already set, the formal trump/kim lunch abruptly canceled. Reporters hastily summoned to a news conference. Sometimes you have to walk and this was just one of those times. Reporter: There had been flashes of hope. Kim Jong-un even took questions from the western press, a first for a north Korean dictator. Chairman Kim, are you ready to denuclearize? If I'm not willing to do that, I won't be here right now. Good answer. Wow. That might be the best answer you've ever heard. Reporter: The president had hoped to parlay his new friendship with Kim into an historic nuclear deal. Instead, he left Vietnam with nothing. Not even a joint statement. He's quite a guy and quite a character, and I think our relationship is very strong. But at this time, we had some options, and at this time, we decided not to do any of the options. Reporter: The president said Kim simply demanded too much. Lifting all sanctions in exchange for dismantling North Korea's largest and most important nuclear facility, but not shuttering the entire nuclear program. Basically, they wanted the sanctions lifted in their entirety, and we couldn't do Reporter: But tonight, north Korea insists that's not true, they said they only asked for some of the sanctions to be lifted. At a press conference, another first, two top north Korean officials told reporters this kind of opportunity may never arise again, saying Kim Jong-un, quote, "May have lost the will for future dealings." Back in Washington, Nancy Pelosi said the president had been played by the north kore dictator. He was the big winner, Kim Jong-un, in getting to sit face-to-face with the most powerful person in the world, the president of the United States. Reporter: Even after the collapse of talks, the president defended Kim over the death of 22-year-old American college student Otto Warmbier, who had been convicted in a show trial. Please think of my family. Reporter: And marched out of court in handcuffs for the whole world to see. More than a year later, he was flown back to the U.S. In a coma, dying just days later. The president seemed to absolve Kim of the any blame. I don't believe that he would have allowed that to happen, just wasn't to his advantage to allow that to happen. Those prisons are rough. They're rough places. He felt badly about it. I did speak to him. He felt very badly. He knew the case very well, but he knew it later. He tells me that he didn't know about it and I will take him at his word. And Jon Karl with us tonight from Hanoi. And Jon, as we know, the president on his way back to the U.S. And to face yet another challenge. His former fixer, Michael Coe on, and his testimony, behind closed doors again today on capitol hill. And Jon, you made news with what you asked the president here in Hanoi. He actually acknowledged watching Michael Cohen from here. He called you a liar, a conman, a racist. What's your response to Michael Cohen? Well, it's incorrect, and, you know, it's very interesting, because I tried to watch as much as I could, I wasn't able to watch too much, because I've been a little bit busy. He lied a lot, but it was very interesting, because he didn't lie about one thing, he said, no collusion with the Russian hoax, and I said, I wonder why he didn't just lie about that, too, like he did about everything else. He lied about so many different and I was actually impressed. So, Jon, the president now goes home to deal with this summit collapse and with Michael Cohen. Reporter: In fact, David, Michael coalen spent another eight hours on capitol hill behind closed doors with the house intelligence committee he will be back again next week and, of course, Cohen has revealed that there are further criminal investigations from the southern district of New York, the U.S. Attorney there. The bottom line, David, the president's Michael Cohen problems are far from over. All right, Jon Karl with us here in Hanoi for days now. Jon, thank you. There is also a developing

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