Transcript for What happened during Trump, Kim Jong Un's historic summit
This has been a very big day in terms of the world. I think it's been -- maybe -- a lot of people are saying it's historic. We're all calling it historic. Even my enemies are calling it historic. Reporter: History made with a handshake. For the first time ever, a sitting U.S. President coming face-to-face with a north Korean leader. Nice to meet you, Mr. President. Reporter: President trump and chairman Kim Jong-un. A man who's been accused of crimes against humanity. How do you trust him, though? Is he willing to change? Do you believe he's changed? Well, you know, over my lifetime I've done a lot of deals with a lot of people. Sometimes the people that you most distrust turn out to be the most honorable ones and the people that you do trust, they are not the honorable ones. Reporter: ABC's George Stephanopoulos sitting down with the president just hours after the summit. Thank you very much, that's fantastic. Reporter: Gaining insights into a day many thought would never happen. Kim Jong-un, known for being a movie buff, saying it was like a scene from a science fiction movie. We will have a terrific relationship, I have no doubt. Reporter: The morning began with smiles and pleasantries. It's easy to forget these two nations just months ago appeared to be on the brink of nuclear war. I feel really great. We're going to have a great discussion. And I think tremendous success. Reporter: The old prejudices and practices worked as obstacles on our way forward, he said, but we overcame them all. President trump the self-proclaimed dealmaker, meeting one on one with Kim Jong-un and two translators. Mr. President, how's it going so far, sir? Very good. What do you think? Very, very good. Reporter: The former reality TV star with a flair for theatrics showing Kim a video outlining the stakes of the summit. 7 billion people inhabit planet Earth. Reporter: The style even reminiscent of a movie trailer. Only a small number -- Reporter: After a working lunch of beef shortkibs, braised cod, and haagen dazs for dessert, president trump showed the northern dic Ator known as the beast. When they emerged the carefully choreographed show continues. Did he agree to denuclearlize, sir? We're starting in that process very quickly. Very, very quickly, absolutely. Reporter: The two leaders signing an agreement aimed, they say, towards peace and denuclearization of the Korean peninsula. We saw you sign the agreement right in this room. You also said you developed a special bond. Describe that bond. Well, it's been a very intense day. And as you know, we discussed things over the last few months. You did, you've spoken -- I have spoken, yes. I've spoken to him, I've spoken to a lot of his people. As you know, his I would say very top person was at the white house last week. We've developed a pretty good relationship in terms of getting something done. It got done. I think it's a terrific document. It's a starter but it's a terrific document. Think far more -- and there are things that we negotiated after that document that are also very important. Like what? We're going to get rid of certain ballistic missile sites and various other things, we're going to put that out later. But we have the framework of getting ready to denuclearlize North Korea. And the freeze in the grumt, complete denuclearization of the Korean peninsula, does that mean that the nuclear umbrella that we have over South Korea is on the table for negotiation? No. That means that they're going to get rid of their nuclear weapons. We never discussed the other. Reporter: President trump boasting that this agreement, though scant on details, is better than the Iran deal he walked away from. Terrible deal. Does that mean any deal with North Korea has to be tougher than the Iran deal? I don't think a deal could be softer. They have to get rid of all their nuclear weapons? They will. I think they will. I really believe that he will. I've gotten to know him well in a short period of time. Denuking. He's denuking the whole place and he's going to start very quickly. I think he's going to start now. They'll be announcing things over the next few days, talking about other missile sites. Because there were, as you know, they were sending out a lot of missiles. Is he going to stop testing? He's going to stop testing. Well, he already has. How many months has it been, George, seven? Where there's been no missiles going up? And he's committed to not starting that up again? He's committed to not do that, that won't be happening. That won't be happening. He means it. He really wants to do something I think terrific for their country. And it's the only way it can be. It's the only way it can be terrific. Reporter: But actually setting up inspections and verification protocol will be extremely complicated. As the two country got through this process, they're going to look at each of the elements of the Kim nuclear program. So that includes rockets, that includes missiles. They're going to look at plutonium generation. What kind of nuclear plants are in operation. To make sure they can't build or create the materials to create these bombs. Did you talk about pulling troops out, U.S. Troops out -- We didn't discuss that, but we're not going to play the war games. You know, I wanted to stop the war games. I thought they were very provocative. I also think they're very expensive. Reporter: Halting war games came as a surprise to the south Koreans. Even more unexpected, an American offer of security. What critics say is too big a gift. This is the only reason that Kim would have come to the table. And it's the real key to whatever progress was made today and whatever progress happens in the future. What other kinds of security guarantees did you offer, put on the table? We've given him -- I don't want to talk about it specifically but we've given him -- he's going to be happy. His country does love him. His people, you see the fervor, they have a great fervor. They're going to put it togethering. And I think they're going to end up with a very strong country. And a country which has people that they're so hard-working, so industrious. If you look at South Korea, someday, maybe in the not too distant future, it will be something like that. You say his people love him. A few months ago you accused him of starving his people. Here's the rub. Kim is a brutal dictator. He runs a police state. Forced starvation, labor camps. He's assassinated members of his own family. How do you trust a killer like that? George, I'm given what I'm given. This is what we have, this is where we are. I can only tell you from my experience. I've met him, I've spoken with him, I've met him. This started very early and it's been very intense. I think that he really wants to do a great job for North Korea. I think he wants to denuke. It's very important. Without that, there's nothing to discuss. How would you score the summit? I think we're safer today than we were three months ago. But I also believe that president trump is deluding himself when he says North Korea is going to give up its nuclear weapons. And deluding himself when he seems to think that he got the better end of the negotiations. Reporter: The reactions today, wide ranging. Praise for president trump's statesmanship. Touting this as a monumental achievement. South Korean president moon jae-in congratulated him in a statement. Yet others calling the summit nothing more than a photo op. Former vice president Joe Biden saying, talking to dictators is one thing, embracing them is another. So far, this is not a deal that advantages the United States or makes us safer. I think one lesson from the past is that imperfect peace processes are better than war mongering. And so even if president trump fails at denuclearlizing north Korea, if he can get back to where we were in some of these past peace processes, then that would be worthwhile. Reporter: Today the president remained confident, firing off a series of self-congratulatory tweets. Got along great with Kim Jong-un, who wants to see wonderful things for his country. As I said earlier today, anyone can make war, but only the most courageous can make peace. But the brutality of the regime even affecting an American college student. University of Virginia student Otto Warmbier was detained for nearly a year and a half for stealing a poster. Please, I have made the worst mistake of my life. Reporter: He was released only to return to the united States in a coma, and would die days later. The president addressed the controversy in a press conference after his meetings. Kim Jong-un, as you know, has killed family members, has starved his own people, is responsible for the death of Otto Warmbier. Why are you so comfortable calling him very talented? Well, he is very talented. Anybody that takes over a situation like he did at 26 years of age and is able to run it and run it tough. I don't say it was nice or I don't say anything about it. I think without Otto, this would not have happened. Something happened from that day. It was a terrible thing. It was brutal. But a lot of people started to focus on what was going on. Including North Korea. Reporter: But can the same man responsible for so many human rights abuses really be trusted as a partner in peace? You trust him? I do trust him, yeah. Now, will I come back to you in a year and you'll be interviewing and I'll say, gee, I made a mistake? That's always possible. We're dealing at a very high level. A lot of things can change, a lot of things are possible. He trusts me, I believe. I really do. I mean, he said openly and he said to it a couple of reporters that were with him that he knows that no other president ever could have done this. I mean, no other -- he knows the presidents. He knows who we had in front of me. He said no other president could have done this. I think he trusts me, and I trust him. Ronald Reagan said, trust but verify. Yeah. Final question, when is Kim coming to the white house? Well, I want to get it along. I want the process to start. I want to see some real work going on, which I believe I will. And I would love to have him at the white house. Whatever it takes. I would love to have him at the white house. And I think he'd love to be there. Reporter: You can watch that full video president trump showed to Kim Jong-un right now. Just click on our "Nightline" Facebook page.
This transcript has been automatically generated and may not be 100% accurate.