Transcript for North Korea expert: 'Big mistake' to assume Kim Jong Un will give up all weapons

Why do you think he decided to free these prisoners now? I really thints to do something. I think he did this because he really wants to do something and bring the country into the real world. I really believe that, Jon. And I think -- I think that we're going to have a success. That was president trump on Thursday talking to our Jonathan Karl after the dramatic release of the three American prisoners by North Korea. President trump saying they're saying Kim is ready to transform his country. But with so little known about Kim and his reclusive regime, how can we be sure? If he's ready to modernize, why now? We're joined by three experts. Su MI Terry. She worked as a specialist at the CIA. Now a senior fellow at the center for strategic and international studies. Jonathan Chang, Seoul bureau chief for "The Wall Street journal." He's reported from inside north Korea. Most recently last fall. Here in the studnos. Of "The new Yorker." He traveled to north kree clast summer. Spent five years in the region as the China correspondent. He's an expert on domestic politics. In this week's issue, he dives into president trump's war on Washington. I want to start with you. Good morning. You were in North Korea last summer. Give us a window into what that was like and what the people there may be thinking about what is happening now. I think they're as bewildered as we are. They have been told for decades that the United States is their enemy. Down the street, there are pictures of missiles going into the U.S. Capitol. And when I talked to schoolchildren, they would say, why is the U.S. Seeking confrontation with us? At the moment, Kim Jong-un is on some level looking to try the change the public narrative. He was on an unsustainable course with the United States. He's taken radical steps to try the change them. President trump says he things Kim wants to bring his country into the real world. Do you think that's really true? Up to a point. There's some truth to that. We know that Kim Jong-un believes his country cannot stay as poor as it is forever. It's poorer than Afghanistan. That's an unstable place. If you're trying to keep your people at bay. He doesn't want to risk a revolution. It would be a big mistake to think he's willing to give up everything to do that. He'll keep whatever he thinks he needs to protect his regime. That may mean his nuclear arsenal. And you recently met with officials from North Korea. What kind of insight did they give you into how Kim is preparing for the summit? They couldn't give me a lot of insight because, you know, they were completely -- confused. I think -- a lot of decision is coming from the very top. Kim Jong-un. Very few people in North Korea. So the foreign ministry is pretty caught up, I would say. I have to agree with Evan. In the terms of modernizing, I do think that Kim Jong-un is looking to be a modern leader of modern North Korea. But it's again, up to a point. Because, is it truly going to be a transformative leader that can change North Korea over the coming years? I question this. I think we should be cautious here. Jonathan, you were at the other historic summit between north and South Korea. What struck you about Kim? I thought it was remarkable how relaxed he looked. Yeah. I agree with that. This is a guy who is in his mid 30s. He hasn't had this sort of experience very much. He had just gone to see XI jianping in China shortly before that. A few weeks. He was looking very comfortable on camera. He knew he would be on the front page of every newspaper the next day. He was joking, laughing, deaf -- deferential in all the right ways. He was very much looking comfortable, in my opinion. And we have seen secretary of state Mike Pompeo now meet two times. There was that smiling picture of Pompeo and Kim. How much groundwork is he setting before president trump arrives? As much as he possibly can. We don't have a whole lot of time before that decision, before trump's decision to meet with Kim Jong-un. Not a lot of time to prepare. Obviously, they're doing that in the back channel. This is why Pompeo went to north Korea and met with him twice now. In a situation like this, you don't want to walk into a meeting and not know exactly what is going to happen. I'm sure they're working on this agreement right now. Before the summit, you know what you're agreeing to. I want to come back to you, Evan. You have a piece this week. Donald Trump's war on the deep state. Which details how the trump administration, you say, is gutting the diplomatic core. How prepared with the U.S. Be in the this meeting? We're coming at this with a much thinner bench than we normally would. On the north Korean side, they have diplomats that have work on this for decades. They can tell you anything going back five or six decades. On the U.S. Side, mass exodus. 60% of the most senior diplomats in the state department have left. 79,000 civil servants have retired or resigned since Donald Trump took office. Miami Pompeo bungled that last week, calling him chairman un, rather than chairman Kim. Was that little equivalent of a typo? Might have been. Time. Pressure. Nobody would think he's not working under incredible stress here. We're operating without a net, these days. Thank you, Evan. Jonathan, finally, to you. What do you think Kim needs to achieve success in his country? I think for this summit, I think what he wants is to come across looking statesmanlike. I thing he's already passed the season with XI and other leaders. Now he's meeting the leader of the free world. North Korea studies the U.S. Closely. They know how Donald Trump is perceived and seen around the world. His goal is to look sincere about what he wants to do, give up nuclear weapons. If he can come away looking like the reasonable one here, he'll have seized the moral high ground. I think that is something that would be a success on his part. If he can do that. Thank you all of you. A fascinating conversation.

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