 -- THIS IS A RUSH TRANSCRIPT FOR 'THIS WEEK' on April 16, 2017 and it will be updated.

(BEGIN VIDEOTAPE)

ANNOUNCER: Starting right now on a special edition of THIS WEEK with George Stephanopoulos: High Alert.

Overnight, North Korea launching another missile. It failed. But these new images have the world on edge. Are they missiles that could some day reach the U.S.? All eyes on the country's unpredictable leader.

And how will President Trump handle this major foreign policy test?

DONALD TRUMP, PRESIDENT OF THE UNITED STATES: North Korea is a problem. The problem will be taken care of.

ANNOUNCER: Martha Raddatz just miles from the North Korean border --

UNIDENTIFIED MALE: (INAUDIBLE) this. I'll be checking here.

ANNOUNCER: -- on the ground with the first line of defense. The service members on high alert. How close are we to confrontation?

MARTHA RADDATZ, ABC HOST: You say the threat is pretty real?

UNIDENTIFIED MALE: It's very real.

ANNOUNCER: Tough questions ahead. Our exclusive interview with Trump's National Security Adviser, Lieutenant General H.R. McMaster.

And expert analysis from across the globe.

From ABC News, a special edition of THIS WEEK. High Alert North Korea. Reporting from Seoul, South Korea, co-anchor Martha Raddatz.

(END VIDEOTAPE)

RADDATZ: Hello, from Seoul, South Korea. It's evening here in this city of 10 million people on high alert on a weekend of escalating tensions. Hours ago, there was yet another North Korean missile launch, the fifth of 2017. This time, it blew up seconds after leaving the launch pad. U.S. officials believe it was likely a medium-range ballistic missile of the kind we have seen before.

But, still, the latest launch rattled nerves, especially after the Sunday appearance Saturday of what could be new long-range weapons at North Korea's big anniversary parade, canisters that appear large enough to house a missile capable of hitting the United States. You can see them there rolling past North Korean leader Kim Jong-Un. Green camo on huge transporters.

If he, indeed, has a missile big enough to reach the United States, and if he can make a warhead small enough to fit on it, will the U.S. be forced the respond?

This hour, all the angles on the most important story in the world right now. And the urgent questions: How far along is North Korea's nuclear program? Are the new missiles we saw at Saturday's parade real? Does Donald Trump have a firm red line? Is there room for negotiation or are Trump and Kim on a collision course?

Vice President Mike Pence arrived here in Seoul today, the start of a ten-day Asia tour. And with China warning both sides to cool it, North Korea is at the top of the administration's agenda. In a moment, we'll talk to Trump National Security Adviser H.R. McMaster, a powerful voice in the president's inner circle. He's in Afghanistan, where the United States just proved what it can do with the "mother of all bomb" strikes on ISIS, a dramatic show of American firepower.

But we begin with North Korea's warning that it will annihilate military bases here in South Korea. They said in minutes if the U.S. tries to take out its nuclear program.

We visited the most important of those front line bases, Osan Air Base, just south of Seoul, 48 miles from the border with North Korea. We got exclusive and unprecedented access.

(BEGINVIDEOTAPE)

RADDATZ (voice-over): If North Korea pulls the trigger this could be target number one -- Osan Air Base, just 48 miles from North Korea, well within range of Kim Jong-Un's existing arsenal of missiles carrying god knows what.

(on camera): So a hardened bunker. This is serious stuff.

UNIDENTIFIED MALE: Yes, ma'am. This is your third set of blast doors here.

(voice-over): The first line of defense is always on guard, 24/7 F-16s on constant patrol. Anti-missile batteries primed and ready.

Behind these concrete walls and steel doors, the top secret and rarely seen operations center, on high alert, watching for any North Korean missile activity.

CO. JAMES BORTREE, 607TH AOC COMMANDER, AIR FORCE: We live with it every day. So -- the nice thing is, for my folks, the mission is staring them in the face.

RADDATZ (voice-over): While the world worries that North Korea will get a missile that can reach the United States, there's though doubt here at Osan the threat is up close, dangerous, and continuous. The slogan here: fight tonight. And you hear it often and always with a sense of pride.

(on camera): There aren't many places I go into where it says Fight Tonight in giant letters. It's a little frightening.

LT. COL. JAMES FIELDS, COMMANDER, 521ST AIR CONTROL SQUADRON: But to -- for us, it's our day to day training. We are always training at that level to be able to fight tonight, because we don't know when that call is going to come.

RADDATZ (voice-over): We visited another top secret facility, the first time ever for a camera crew. If a missile is aimed at South Korea, the job here, blow it out of the sky.

North Korea has conducted just five underground nuclear tests in the last 10 years, but missile launches are far more common -- several this year alone, every one closely monitored on these screens, including last night's failed launch.

(on camera): What's it like in here when a ballistic missile is launched?

COL. MARK HOLLER, COMMANDER, 15TH AIR DEFENSE ARTILLERY: Well, you would think it would be hectic, but due to the level of training of the soldiers here, it's actually a pretty calm exercise. I would compare it to maybe an air traffic controller tower.

RADDATZ (voice-over): Right next door, rows and rows of bunk beds. If war comes to South Korea, the staff will sleep right here.

LT. GEN THOMAS BERGESON, DEPUTY COMMANDER, U.S./U.N. FORCES, KOREA: And it allows us to do continuous operations for an extended period of time.

RADDATZ: And you've got food, you've got everything you need.

BERGESON: We have food, showers, latrines.

RADDATZ (voice-over): Lieutenant General Thomas Bergeson is deputy commander of all U.S. and U.N. forces in South Korea.

(on camera): What concerns you most?

BERGESON: So our biggest concern is that he's going to miscalculate. That's always the number one concern. So we want to make it crystal clear to the North Korean leadership that this would be a completely futile endeavor were he to challenge this strong, iron-clad bilateral alliance.

RADDATZ: Because we have a new president and he, no doubt, Kim Jong-Un wants to test him in the same way...

BERGESON: Right.

RADDATZ: -- that dynamic works, is this, from your time here, from watching here, one of the more dangerous times?

BERGESON: I would say that there's -- certainly you can feel the tensions. Very clearly, this is serious and they need to know that we are prepared and that this defensive alliance is strong and ready to fight tonight.

RADDATZ: Part of that defense, Patriot Missile batteries.

LT. COL. MARK PELINI, BATTALION COMMANDER, 652ND AIR DEFENSE ARTILLERY: And you'll notice here in Korea, we keep our launchers loaded with live interceptors at all times so that we're ready to fight tonight.

RADDATZ: Tell me a little bit about the batteries, just in terms of what they can stop, how they stop them, how that works.

PELINI: Yes. Well, the -- this weapons system is capable of defeating a wide range of enemy capabilities from unmanned aerial systems to short-range and even long-range ballistic missiles. This battery is capable -- is designed to search for, detect and engage those inbound ballistic missiles.

RADDATZ: At Osan, they're confident in this system, claiming the success rate of the Patriot is nearly 100 percent.

PELINI: And it's a bullet on bullet scenario, where the Patriot missile hits the threat missile and destroys it.

RADDATZ: A few miles from the Patriots, out on the flight line, are the Growlers.

COL. ANDREW HANSEN, COMMANDER, 51ST FIGHTER WING AND INSTALLATIONS: So they have jamming capability, electronic jamming capability, so they can deny the enemy the capability to launch surface-to-air missiles at our aircraft.

RADDATZ: Facing that threat, Major Shawn Wallace, an F-16 pilot, up in the skies training at least three times a week, within miles of the North Korean border.

MAJOR SHAWN WALLACE, F16 AIR PILOT: And you get to see the stark contrast, because as the lights start to come on and you fly along the DMZ, you can look out one window and it's as bright as day, with the city of Seoul and then all of South Korea.

And then you look out the other side of your cockpit, and it is just darkness.

RADDATZ: But make no mistake, it's that darkness which causes concern, the lack of hard intelligence, the unpredictability and the war of words right now have created a region on edge.

(on camera): Kim Jong-Un is basically saying that he could strike and take out any of the American military bases.

Could that happen?

BERGESON: No. No, they could try, but as you saw today, out here, you have air defense artillery brigade and they have the technology and the capability and they're ready to intercept those kinds of missiles.

So they could try. It would be futile.

(END VIDEO TAPE)

RADDATZ: And we're back here now live in Seoul.

I'm joined by ABC News contributor, Colonel Steve Ganyard, a retired Marine Corps fighter pilot and former deputy assistant secretary of state -- and Steve, talk to us about the failed missile launch first.

What do we know about that missile?

COL. STEVE GANYARD, ABC NEWS CONTRIBUTOR: It's going to take us a while to figure out, Martha, what the actual kind of missile it was, because it blew up so quickly after launch, we aren't going to have much radar telemetry data. So it will take the intelligence analysts a little while to figure out what kind it was.

But we also can't be too complacent. Even though it's failed, it does show that they're determined to perfect these missiles and develop a long-range missile capability.

RADDATZ: And I suppose a real concern from this weekend is the parade and the missiles that we spotted in that parade. We don't know if they're real, but they appeared to be long-range missiles.

GANYARD: Lots of concerning things coming out of that parade. The first is the size of some of those missiles . So, bigger size means longer range, better chance of getting all the way to the United States.

Also the diversity of missiles that we saw, not just land-based, but we saw sea based, submarine launched missiles. Some of those missiles looked very much like a DF-31, which is a sophisticated Chinese missile. So, lots of questions coming out of that, lots of things to worry about.

But the real takeaway I think is range. For decades, presidents, both Republican and Democratic, have been able to kick the can down the road on North Korea because there's never been an ability to reach the United States. What we saw there yesterday in that ma raid, those missiles that theoretically could eventually reach the continental United States, which is why president Trump thinks he needs to take on the North Korean challenge here and now.

RADDATZ: And of course the nuclear tests that they are still expecting to launch that underground nuclear test. Is there anything that can be done to stop that, to deter them from doing that?

GANYARD: There are a couple of options. One we would call kinetic, and one we would call nonkinetic. We saw in Afghanistan that mother of all bombs. There's actually a bigger bomb in the U.S. inventory by weight, 30,000 mounds, and it's called a MOP, massive ordnance penetrator. And it is designed to go down deep, penetrate 200 feet of reinforced concrete and take out any kind of underground bunker. So that would be the kinetic option.

There's a new Buck Rogers kind of options, it's called a high-power microwave. It would be delivered by a stealthy cruise missile and send an intense burst of electromagnetic energy over that test site, which would go down wires and fry anything underneath the ground. So, nobody gets hurt, but everything gets disabled.

So, the president has a new arrow in his quiver, both kinetic and nonkinetic options here for any kind of an underground nuclear test.

RADDATZ: And Steve, what do you think the reaction would be from North Korea if there was a preemptive strike?

GANYARD: North Korea has been quite clear that if there's any kind of military action on North Korean soil that they will retaliate in some way, but the problem is, is that that retaliation is going to occur on South Korean soil, or at Japan, which means that we need to very closely coordinate with our two closest allies in the region before thinking about any kind of a military action.

RADDATZ: And Steve, very quickly, the North Korean – our intelligence in North Korea is pretty bad. Why is that?

GANYARD: We just have very little human intelligence on the ground. It's a closed, Stalinist society. So, even the internet is controlled. So we get very little information.

Yesterday was very reminiscent of those days of the Soviet days when we would wait for those May Day parades to try and discern what the Soviet Union was doing, what they were thinking, but this is something that's going to continue to bedevil us in terms of North Korean intelligence.

RADDATZ: Thanks, Steve, for all your insight.

President Trump faces major decisions when it comes to dealing with North Korea. And the man who will help him make those tough calls is his top National Security Adviser H.R. McMaster. We'll talk to him in an exclusive interview about how he'll advise the president on that and other national security challenges coming up in just two minutes.

(COMMERCIAL BREAK)

(BEGIN VIDEO CLIP)

RADDATZ: Mr. Trump, do you have a red line with North Korea? Would you consider military action? And how far would you let them go?

TRUMP: We have tremendous -- has been just sucked out of our country by China. China says they don't have that good a control over North Korea. They have tremendous control. They have total, absolute control practically of North Korea. I would get on with China. Let China solve that problem. They can do it quickly and surgically. That's what we should do with North Korea.

(END VIDEO CLIP)

RADDATZ: That was then-candidate Donald Trump during the New Hampshire Primary debate, saying that China should take care of North Korea. Back then, it was a hypothetical. Now it's a reality. So what's President Trump's position today? His National Security Adviser H.R. McMaster joins me now from Afghanistan.

It’s good to see you, General McMaster. We will get to your trip in Afghanistan in a moment, but let’s talk about North Korea.

We know the missile test failed. What can you tell us about that? How long will it take to determine exactly what happened there?

H.R. MCMASTER, NATIONAL SECURITY ADVISER: Well, thanks, Martha. It’s a privilege to be with you.

Well, this latest missile test, it just fits into a pattern of provocative and destabilizing and threatening behavior on the part of the North Korean regime. And I think there’s an international consensus now, including -- including the Chinese and the Chinese leadership -- that this is a situation that just can’t continue. And the president has made clear that he will not accept the United States and its allies and partners in the region being under threat from this hostile regime with nuclear weapons.

And so we’re working together with our allies and partners, and with the Chinese leadership, to develop a range of options. And the president has asked the National Security Council to integrate the efforts of the Department of Defense, State, our intelligence agencies, so we can provide options and have them ready for him if this pattern of destabilizing behavior continues, and if the North Korea regime refuses to denuclearize, which is the accepted objective of both the United States and Chinese leadership, as well our allies in the region.

RADDATZ: I want to go back to the missile, if I could, for a moment. Apparently it was a medium-range ballistic missile.

But can you talk a little bit about what we saw during the parade in North Korea and the missiles they displayed there? Are they real? Was that an ICBM?

MCMASTER: Well, I’m not -- I don’t know, Martha, I’ve not been in touch with our intelligence community on that, so I would just defer to our intelligence communities and the Department of Defense on that particular question.

Of course, the purpose of that parade is to sort of demonstrate military prowess in a threatening way, and so whether those weapons or real or fake is -- is unclear I think to -- at least -- I saw it on a television, like you did, Martha.

Of course, the purpose of that parade is to sort of demonstrate military prowess in a threatening way. And so whether those weapons are real or fake is unclear I think -- at least to -- I saw it on television like you did, Martha. Or no, you saw it -- you saw it better than I did. You were -- I think you were close by, just in South Korea.

RADDATZ: Yes, I was a little closer than you were.

Let’s go back to what you were saying before, and today a White House foreign policy adviser briefed reporters on Vice President Pence’s flight to Seoul and said, had North Korea tested a nuclear weapon, other actions would have been taken by the U.S. You hinted at some of that.

What would have happened? What was he talking about?

MCMASTER: Well, the president has made very clear that he is not in the business of announcing in advance exactly what he’s going to do in any particular situation. And I think what you saw last week with the president’s decisive response to the Assad regime, to mass murder of innocent people, including children, with chemical weapons, that this national security team is capable of rapidly responding to those sorts of crises or incidents and events and providing the president with options. And our president is clearly comfortable making tough decisions and respond.

RADDATZ: But the military option’s still on the table?

MCMASTER: Well, all our options on the table undergoing refinement and further development.

RADDATZ: And how close do you think North Korea is to having a nuclear weapon capable of reaching the United States?

MCMASTER: Well, you know, estimates in these sorts of things vary widely. What is clear is, as long -- as long as their behavior continues, as long as they continue missile development -- even though this was a failed missile, they get better and they learn lessons. So what’s critical is for them to stop this destabilizing behavior, stop the development of these weapons, and denuclearize. And that is the best interests of everyone in the region, and ultimately it’s in the best interests of the North Korean people as well.

RADDATZ: North Korea’s Vice Foreign Minister said Friday that the Trump administration is more vicious and more aggressive than the Obama administration, saying that Trump’s aggressive tweets were making trouble.

Does the aggressive language increase the likelihood of conflict?

MCMASTER: I think it should make clear to the North Korean regime that it is in their best interest to stop the development of these weapons, to stop the development of these missiles, and to denuclearize the peninsula. And so I think while it’s unclear -- and want to -- do not want to telegraph in any way how we’ll respond to certain incidents, it’s clear that the president is determined not to allow this kind of capability to threaten the United States. And our president will take action that is in the best interest of the American people.

RADDATZ: You know, one of the big concerns here, General McMaster, is how North Korea would respond to aggressive action or some sort of preemptive strike. How do you think they would respond?

MCMASTER: Well, that’s what particularly difficult about -- about dealing with this regime, is that it is unpredictable. This is someone who has demonstrated his brutality by murdering his own brother, by murdering others in his family, by imprisoning large numbers of people in horrible conditions for no reason, for political reasons. So this regime has given the world reason for concern. And that includes -- that includes the Chinese people and the Chinese leadership as well.

I mean, what Kim Jong-Un is doing is a threat to all people in the region and globally as well. I mean, this is someone who has said not only does he want to develop a nuclear weapon, but he wants to use it to coerce others. He’s said that he was willing to proliferate nuclear weapons once he develops them. And so this a grave threat to all people.

RADDATZ: You know, you heard what President Trump said about China in that primary debate, but this week he said, after listening to President Xi, he realized it’s not so easy. Are you truly confident you can get China to pressure North Korea in a meaningful way?

MCMASTER: Well, we’ll see what happens. What we do know is that, in the midst of responding to the mass murder of the Syrian regime, the president and the first lady hosted an extraordinarily successful conference, summit, with President Xi and his team. And not only did they establish a very warm relationship, but since that time they’ve worked together on other issues. On North Korea they worked together. But they worked together as well in connection with the response to the mass murder on the part of the Assad regime in connection with the U.N. vote. I think President Xi was courageous in distancing himself from the Russians, isolating really the Russians and the Bolivians.

And this all occurred on the same day that President Trump hosted the Secretary-General of NATO, representing our wonderful NATO allies. And I think the world saw that, and they saw, well, what club do you want to be in? The Russian-Bolivian club? Or the -- in the club with the United States, working together on our mutual interests and the interests of peace, security.

And I think it was just a great week of the United States, in thanks mainly to our president’s (INAUDIBLE).

RADDATZ: You know, you sound very confident. President Trump of course sounds very confident. But one final question on this: every president since Bill Clinton has said the U.S. will not tolerate a nuclear armed North Korea, and North Korea has only grown stronger in their capabilities. So why do you think President Trump will have a different outcome?

MCMASTER: Well, as you mentioned, this is a problem that has been passed down from multiple administrations. But our president, I think, it’s really the consensus with the president, our key allies in the regions -- Japan and South Korea in particular, but also the Chinese leadership -- that this problem is coming to a head. And so it’s time for us to undertake all actions we can, short of a military option, to try to resolve this peacefully.

And so we’re going to rely on our allies like we always do, but we’re also going to have to rely on Chinese leadership. I mean, North Korea is very vulnerable to pressure from the Chinese. Eighty percent of North Korea’s trade comes from China. All of their energy requirements are fulfilled by China.

So in the coming weeks, months, I think there’s a great opportunity for all of us -- all of us who are really the threat now of this unpredictable regime -- to take action short of armed conflict, so we can avoid the worst.

RADDATZ: And I want to turn to Russia and Syria. Secretary of State Rex Tillerson visited this week and said relations were at a low point but the president tweeted Thursday, “Things will work out fine between the USA and Russia. There will be lasting peace.”

What suddenly gives him that confidence?

MCMASTER: Well, when relations are at the lowest point, there’s nowhere to go but up, Martha. So -- so I think the secretary's visit to Russia was perfectly timed. You know, Russia has given support to a murderous regime in Syria that has perpetuated a civil war and as cycle of violence that, along with obviously the brutal -- the brutal efforts of and actions of ISIS, have brought suffering to so many people, have created a crisis within Syria that has bled over into Iraq, and of course has bled over into neighboring countries and into Europe and so forth.

And so Russia’s support for that kind of horrible regime, that is a party to that kind of a conflict, is something that has to be drawn into question.

RADDATZ: Do you --

MCMASTER: As well as Russia’s subversive actions in Europe.

And so I think it’s time though, now, to have those tough discussions Russia. And there’s nobody to do it than our Secretary of State.

And then also to find areas of cooperation.

RADDATZ: Do you think we need ---

MCMASTER: Where do our countries align?

RADDATZ: -- more U.S. troops in Syria?

MCMASTER: What can we accomplish together?

Well, I mean, that remains to be seen. I don’t think so. I think what we’re doing now is supporting partner forces in Syria, in certain portions of the country, including the northeastern part of the country along the Euphrates River valley. It is a matter of time only until ISIS is defeated there. And what’s going to be really critical though is what forces can then establish enduring security in those regions that have a legitimacy with the population, that are representative of the population, that can set conditions for reconstruction to begin.

Martha, the cities of the Sunni Arab world in that region are in rubble. And so in a very successful conference in Washington two weeks ago, the United States State Department organized a bunch of donors and like-minded allies, part of coalition to pledge money for reconstruction. But what we need now is we need a security situation that’s conducive to that reconstruction, that can allow so many of these displaced people and refugees to return. And for those long-suffering people to enjoy the security, stability, that they deserve.

RADDATZ: And I want to finish on your trip there to Afghanistan. It’s really remarkable to think about the fact that we’ve been fighting there since 2001. What haven’t we done that we should have? And do you think more troops are needed there as General Votel has said?

MCMASTER: Well, I think what this long campaign here in Afghanistan shows is that the future course of events in war depends not on what you decide to do, but also on the actions of your enemies. And so what we’ve seen here is an interaction between ourselves, our NATO and other partners here, and especially our Afghan partners, and very determined and brutal enemies.

And so what has happened in recent years, at a period of our maximum effort, we didn’t have as reliable a partner in the Afghan government as we would’ve liked. Now we have a much more reliable Afghan partner and we have reduced to considerably the degree and scope of our effort.

Our enemy sensed that and they have redoubled their efforts and it’s time for us, alongside our Afghan partners, to respond.

And so what’s clear in here in Afghanistan is the stakes are high. I mean, this is -- this is really the modern-day frontier between barbarism and civilization. And so with those high stakes in mind, recognizing that the Taliban groups that we’re fighting here, that the ISIS groups that we, alongside -- really the Afghan forces are really fighting and we’re just enabling them -- in the eastern part of the country, are a threat to all civilized peoples.

And so really what we do from this point on is going to depend on the decision that the president makes, and he’s asked our team to integrate the efforts of the various departments, because what we haven’t had, Martha, really here is a very well stitched-together effort that combines what we’re doing politically and diplomatically and militarily and economically and through -- with our Treasury and Commerce departments in the areas financing the economy -- so that hasn’t been stitched together as well as it might have, along with the efforts our multinational partners.

So that’s what we’re assessing now and the president has asked for a range options, and we’ll give him those options. And we’ll be prepared to execute whatever decision he makes.

RADDATZ: OK, we’re going to have to leave it there.

General McMaster, it was great talking to you. Thank you.

MCMASTER: Great talking with you, Martha. Thank you.

RADDATZ: Up next, most Americans know very little about life inside the secretive nation of North Korea. One person who does is ABC's Bob Woodruff. He'll bring us his insights next.

Plus, the former U.S. ambassador to South Korea, Chris Hill, joins us as the U.S. and South Korea conduct joint military exercises. We'll discuss what options America has to respond to this crisis.

(COMMERCIAL BREAK)

RADDATZ: North Korea's capital, Pyongyang, is just about 120 miles away from here, but a place few Americans have seen firsthand. My colleague Bob Woodruff recently returned from his eighth trip to North Korea since 2005, bringing us rare insight into life inside the isolated country and its regime's pursuit of a nuclear weapon.

(BEGIN VIDEOTAPE)

BOB WOODRUFF, ABC NEWS CORRESPONDENT (voice-over): Pomp and circumstance taking over part of Pyongyang this week. And in the midst of all the military tension between North Korea and the U.S., Kim Jong-Un, cheered on by a dense crowd, showing off a more modern Pyongyang.

This scene, a stark contrast from when I first arrived the nearly deserted capital city in 2005.

(on camera): But we expect to show you a country that the world knows very little about.

(voice-over): And we did. From our visit to the Children's Palace where your Koreans are trained in sports and music, to their subway system.

(on camera): You can see that this design is some old 30-year-old kind of design.

(voice-over): And to my aerial tour of Pyongyang in 2016.

(on camera): It was amazing. We saw a chance not only to see the cooperative farms as we came in over the suburban area, but also into the town. We had never seen this entire city before.

(voice-over): On my first trip here, we traveled two hours outside the capital to a collective farm, where I met with North Koreans skeptical of the United States.

(on camera): What do on you think about the Americans?

(voice-over): Back then, that 18-year-old told us he thought Americans were the sworn enemy of the Korean people.

(on camera): Have you ever met an American before?

(voice-over): No, he said, he hadn't.

(on camera): I'm an American.

(voice-over): As for what might be behind some of that animosity, the North Korean people, largely cut off from the rest of the world, and prevented by their government from having contact with our country. Most Americans have never traveled there.

That exchange is still limited, but recently, ABC News caught up with a high profile defector from North Korea, the former deputy ambassador to the United Kingdom. He said one of the biggest misconceptions is just how cruel the regime can be.

UNIDENTIFIED MALE: They cannot understand that the North Korean system, it is itself, it's a kind of slavery system. I think one day when North Korean system, you know, the collapse, I think the whole world will be shocked.

WOODRUFF: The country has also provided limited firsthand knowledge of its nuclear progress. In the time I've been covering North Korea, we have put in multiple requests to tour the nuclear facilities that have dominated U.S. headlines.

(on camera): So what do we have here?

(voice-over): In 2008, we were the first members of the media allowed inside Yongbyon nuclear facility.

(on camera): So what we're seeing now inside this room is actually the cold water, just covered by ice, and underneath there is about 1,500 uranium rods.

(voice-over): But our most recent request, like many others, denied.

(on camera): We put in all sorts of requests to visit out here, the launch locations where the missiles are being launched.

(voice-over): Instead, they took us deep into the country to showcase another proud achievement, their high-end ski resort.

(on camera): Are there any other guests, you think?

(voice-over): An eerily empty expanse where skiers take the slopes in time to the patriotic music.

Carefully choreographed scenes have been a constant in my visits here, including those now iconic military parades, like this one in 2010, Kim Jong-Un making his public debut back when he was known as the Young General.

(on-camera): Now that the music stopped, which was really loud, now it's completely silent. Because right up there, Kim Jong-Il and his son, Kim Jong-Un, will come out and watch.

(voice-over): Now, the eyes of the world watching and waiting to see Kim Jong-Un's next move.

For THIS WEEK, Bob Woodruff, ABC News.

(END VIDEOTAPE)

RADDATZ: And they certainly are here in South Korea. Our thanks to Bob.

Up next, the man who sat face to face with the North Koreans at the nuclear negotiating table. Former U.S. ambassador to South Korea Christopher Hill joins me. And later our panel of experts on what President Trump's stalled domestic agenda may mean for his actions on the world stage.

(COMMERCIAL BREAK)

(BEGIN VIDEO CLIP)

MIKE PENCE, VICE PRESIDENT OF THE UNITED STATES: This morning's provocation from the north is just the latest reminder of the risks each one of you face every day. Our commitment to this historic alliance with the courageous people of South Korea has never been stronger. And with your help, and with God's help, freedom will ever prevail on this peninsula.

(APPLAUSE)

(END VIDEO CLIP)

RADDATZ: Vice President Mike Pence at a U.S. army base in Seoul earlier this evening, attending an Easter meal with U.S. and South Korean troops. His trip to South Korea and Japan coming as our allies in the region wonder how the U.S. will respond to the North Korean threat.

Veteran diplomat Christopher hill joins me to discuss that next.

(COMMERCIAL BREAK)

(BEGIN VIDEO CLIP)

BILL CLINTON, 42ND PRESIDENT OF THE UNITED STATES: North Korea cannot be allowed to develop a nuclear bomb. We have to be very firm about it.

GEORGE W. BUSH, 43RD PRESIDENT OF THE UNITED STATES: We will not settle for anything less than the complete, verifiable, and irreversible elimination of North Korea's nuclear weapons program.

BARACK OBAMA, 44TH PRESIDENT OF THE UNITED STATES: We stand with our ally, South Korea, and insist that North Korea keeps its commitment to abandon nuclear weapons.

(END VIDEO CLIP)

RADDTAZ: For decades, American presidents and their advisers have grappled with how to stop North Korea's nuclear program, including our next guest Christopher Hill, the former U.S. ambassador to South Korea. Under President George W. Bush's administration, he headed up the U.S. delegation to the six-party talks to resolve the North Korean nuclear crisis, and he later served as U.S. ambassador to Iraq.

Ambassador Hill, thanks for joining us.

CHRISTOPHER HILL, FMR. U.S. AMBASSADOR TO SOUTH KOREA: Pleasure.

RADDATZ: When you were head of the delegation at the six-party talks, North Korea lied, obfuscated, and then pursued more missile tests, and as we saw they've continued to do that.

Why should President Trump expect anything different?

HILL: Well, first of all, the importance of negotiating with them in the six-party context was to force China to take a role, and of course, they were in the chair of this whole process.

But secondly, and I think this brings us to the present day with Vice President Pence's trip, it was important to show the South Koreans that will be do everything we can, including negotiating. And so the days where the U.S. would negotiate with North Korea and leave the South Koreans at the airport wondering what was going on, those days are over. And we worked very closely with South Korea. And I think in the process brought the U.S. and South Korea together.

As for the North Koreans, you bet it's a tough proposition. But I agree with all those presidents you just showed that we cannot allow them to develop a nuclear weapon.

RADDATZ: From what you've seen of the Trump administration, and I know you listened to General McMaster there, what are you hearing that is encouraging you besides what you just talked about with Vice President Pence?

HILL: Well, first of all, it is very encouraging that they are in close contact with the Chinese, that they seem to be trying to work things together with China. That seemed to be an elusive concept at a certain point in time. And yet that, I think, is very much happening.

Secondly, of course, is the vice president's visit because South Korea has some 20 million people within artillery range of North Korea. And they essentially worry about two things. They worry about a preemptive action by the U.S. where they weren't included in it. They also worry about talking to the Chinese kind of over their heads. And they kind of take the view, look, there shouldn't be anything about us without us.

And so I think the effort to kind of clue them in, to be close to them, to listen to them, to discuss the strategy, I think is very crucial. I would like to see, at some point, a U.S. ambassador named to South Korea, but I guess that takes a long time for this administration.

RADDATZ: I guess that's taking a long time in several places. Let's go to President Trump, though. You have mentioned others. You have mentioned the vice president. He has had some very aggressive language. Does that help or make it more difficult?

HILL: Well, I think he's trying to out-North Koreans the North Koreans. So let's see if that works. Certainly it makes people nervous when they're not quite sure what he means by it. And, you know, great powers can't really bluff.

So when you talk in those terms, you have got to be prepared to back it up. And I guess that's what worries people the most.

That said, I certainly appreciate the fact that he has understood this is a major issue. I mean, if I were President Trump, I wouldn't want to go before the American people in 2020 and say, well, you know, we gave it the junior college try and we decided there is nothing we can do about this.

RADDATZ: And when you look at what's happening now and throughout these past presidents, it's very dangerous today. I mean, everybody I have talked to says the threat is very different now because they are close to getting a nuclear missile on an ICBM.

When you look at it, how tense do you think everyone should be?

HILL: I think it is -- we have come to a moment where this is kind of different from the past. First of all, they have had over 25 missile tests. They're working on a whole new generation of missiles. Of course, one of them failed in the last 24 hours. But that doesn't mean they'll try again.

So it's a new generation of missiles. And clearly, they're working on a warhead design for nuclear devices. So this is, I think, a very serious matter. And it's coming down the tracks.

And people often take the view, well, somehow, this is all about their regime survival. This is how they'll survive being a nuclear weapons country. Actually, I think they're more ambitious about it. They see this as a means to somehow decouple the U.S. from its ally in South Korea, from its ally in Japan, and somehow create a situation whereby, at least in theory, holding the U.S. at risk, the U.S. would be less willing to participate in a conflict on the Korean Peninsula, were it to come to that.

So they have ambitious plans for this. And I think we need to be very clear about the need to stop them. And I'm particularly discouraged when I hear people talking about, well, maybe we can freeze their tests in return for freezing our exercises with South Korea.

That is not going to get us in the right direction at all.

RADDATZ: OK. Well, we hope we go in the right direction. Thanks very much for joining us, Ambassador Hill.

Up next, what does the threat from North Korea and how Trump responds mean for his agenda back home? Our expert panel of reporters weighs in.

(COMMERCIAL BREAK)

RADDATZ: How are President Trump's actions abroad playing on the world stage and affecting his domestic agenda? Joining me in Washington are ABC News political director Rick Klein; and Jennifer Jacobs, White House reporter for Bloomberg Politics; and here in South Korea, Jonathan Cheng, The Wall Street Journal's Seoul bureau chief.

Welcome to all of you. And I want to start with you, Jonathan, because you're right here next to me. You called North Korea's missile launch today a sign of their confidence in the face of President Trump's warning. What do you mean by that?

JONATHAN CHENG, SEOUL BUREAU CHIEF, WALL STREET JOURNAL: Well, I think it definitely shows that Kim Jong-Un is not going to be cowed when President Trump, arguably -- probably the world's most powerful man, has been saying that if you do anything that crosses the line, we're going to act. That hasn't stopped them from wheeling out what may be as many as three new ICBMs. It hasn't stopped him also from trying to launch --

(CROSSTALK)

RADDATZ: So they're not believing Trump's aggressive talk?

CHENG: I don't know that it's not believing. But North Korea is a small country and it has been wedged here between China, between Russia, between the U.S., Japan, all these powers. And the way it's been able to survive for so long in part has been by charting its own course and doing things against the grain. We don't know what they're going to do.

RADDATZ: OK, Jennifer, I want to go back to you and the word from Washington. There was a poll out Friday through CBS News that 56 percent of Americans are uneasy about Trump's ability to deal with this. Not a good sign, Jennifer.

JENNIFER JACBOS, WHITE HOUSE REPORTER, BLOOMBERG NEWS: Yes, you're exactly right. There is substantial unease. And it's -- it's almost like Americans are on a little bit of overload with the bombs on Syria last week and the big bomb in Afghanistan this week. So they're just not sure what Trump is thinking on North Korea. They're on overload.

But I can give you a little bit of a window. I know that his national security team put together various scenarios based on how they thought that North Korea would behave this weekend, and what their reactions to that would be. And I'm told that when this medium-range missile fizzled right after launch, that Trump decided pretty quickly to just downplay it.

I can also tell you a few other quick things, that I'm told that Trump is not into regime change, regime removal for North Korea. He's not thinking about removing Kim Jong-Un from power. He's not thinking about reunify -- trying to unify the two Koreas. That's not on his mind. I'm also told, you know, the word kinetic comes up a lot, that he is definitely willing to carry out kinetic military action. A sudden attack.

But the key thing here, and you heard this a lot in your interview with General McMaster, Martha, is China, China, China. I was told by one adviser that the president has said North Korea is a Chinese problem located in North Korea.

RADDATZ: OK, Rick Klein. But all the talk of national security -- and it seems like all we've talked about for a couple of weeks here. Let's go back to the domestic agenda of President Trump. And he's not really making much progress there -- health reform, tax reform, the travel ban stuck in the courts. So what's up?

RICK KLEIN, ABC NEWS POLITICAL DIRECTOR: Well, if there is a Trump doctrine, the president is stumbling into that doctrine.

And the context that you mentioned is critical here. We're coming up on the end of that critical first 100 day period, and he is striking out. Nothing going on health care, tax reform, infrastructure. None of these things is moving. But the hope among Capitol Hill Republicans actually is that these things are connected. And what I've heard from several member of Congress on Capitol hill is that this Trump as commander in chief, the actions on the world stage, they are bucking up the mood among Republicans.

At least for now. It's very tentative. And I'll tell you, they have given up on trying to figure out what President Trump really believes because of the recent shifts in policy and just how fast-moving all of these actions on the world stage are.

But the hope is that these things are connected, and that this viewing of President Trump as commander in chief, tackling world problems, that could have a spillover effect on the legislative agenda and they could put some more points on the board domestically.

RADDATZ: And Jennifer, I want to ask you about the flip fops we've heard. Is that really saying much about his strategy, or is it just the reality of governing?

JACOBS: Probably just the reality of governing. I mean, one striking thing here is that he's listening to his career staff. That's -- he's been almost establishment in his actions and his thinking with this. But, you know, his staff had been arguing that these were not shifts so much as, you know, concessions in his favor. For example, I was told that in his meetings where the NATO Secretary General, that he was very, very firm, very pushy about wanting, you know, more money for defense. More participation in fighting terrorism. And that he's getting his way on those things. On China, on the currency manipulation, there was this new report out from the Treasury Department this week that very specifically said that none of our trading partners could meet the criteria right now to be labeled a currency manipulator.

So again he's listening to his career staff right now, which is unusual.

RADDATZ: And, Rick, is he listening to Republicans on the Hill? IS he listening to his base?

KLEIN: It's quite the time for on-the-job training. Now, the base and Republicans on the Hill, those are two very separate things. If you look at the way that he has been moving, despite all of the talk about broken campaign promises, he's actually moving closer to the mainstream of the Republican Party. Maybe even the broader, bipartisan mainstream about America's role in the world.

That heartens a whole bunch of Capitol Hill Republicans. Who -- the people that have heartburn over this are more of this core base. And that includes members of the Freedom Caucus, some Libertarians who say what is it with this -- all this foreign adventurism?

The same goes really for the staff shakeup that we hear about so much and the attention right now on Steve Bannon getting sidelined. There's an interesting twist for the potential for Steve Bannon to be set off to the side. The fact is, a lot of members of congress would privately cheer that on the Republican side. Steve Bannon is not liked widely by members of Republican leadership. In fact, many of them are getting close contacts now and good relationships with Jared Kushner.

So, it could be that these internal staff shakeups actually help President Trump even though they are not good headlines, they help with his relationships on Capitol Hill.

RADDATZ: And Jonathan, I wanted to talk to you again about here on the Korean peninsula. We started the program that way. We end the program this way. What do you expect here next? I mean, when I walk around the city, people are not frightened. Pretty are pretty calm. People are pretty used to it. But you heard us talk today, it is at a very, very serious stage.

CHENG: You're right, the South Koreans are used to this. They have lived in the shadow of the North Korean threat for 50, 60, 70 years. It's not unusual for them to hear these bellicose remarks from the North.

What they aren't used to is hearing it also from the White House. And if you're a South Korean here, you're looking at a neighbor that is perhaps on the verge of something big happening here. And it may start there, and it may start from Washington. And you feel a little bit caught in the cross fire.

RADDTAZ: So they're more nervous when they hear this aggressive talk?

CHENG: I think so. Again, usually, the White House, Washington, has been a reassuring force. I think that's why Mike Pence is here. In a certain I think he's here to reassure the allies. But you have Trump tweeting and -- sometimes going quite wild in his rhetoric from one side to the other, and it's unclear what exactly he intends to do.

RADDATZ: And does it seem to you, quickly, that he has a red line?

CHENG: Well, I don't know what that red line is. And I don't know that North Korea has gotten the message either. And I think south Korea, here, too, is concerned that nobody knows right where this is.

RADDATZ: OK. We'll have to watch -- we'll have to check back in with you again. Thanks you for joining us. Thanks to all our panel. We'll be right back after this from our ABC stations.

(COMMERCIAL BREAK)

RADDATZ: That's all for us today from atop the Vista Walker Hill Hotel in Seoul. Thanks for sharing part of your Easter Sunday with us.

Check out "WORLD NEWS TONIGHT", and have a great day and a great Easter.