After the Summit: A Next Step for the United States and North Korea

July/August 2018
By Stephen Herzog

The improved prospects for peace and nuclear disarmament dominated the headlines following the historic first meeting between the leaders of the United States and North Korea, countries that have been bitter adversaries for seven decades.

U.S. President Donald Trump shakes hands with North Korean leader Kim Jong Un at the start of their historic summit at the Capella Hotel on Sentosa Island in Singapore on June 12. The challenge will be to implement their summit declaration, including the “complete denuclearization” of the Korean peninsula. (Photo: Saul Loeb/AFP/Getty Images)The about-face by the two leaders at the June 12 summit in Singapore was remarkable, given that their bellicose rhetoric mere months earlier had threatened to bring the world to the brink of nuclear war. “We’re prepared to start a new history, and we’re ready to write a new chapter,” declared U.S. President Donald Trump. “The world will see a major change,” affirmed North Korean leader Kim Jong Un.1

Their summit joint statement, however, signed after four hours of talks, is vague and draws on wording from past U.S.-North Korean communiqués. Regarding nuclear weapons, North Korea signed on to familiar diplomatic language about the “complete denuclearization” of the Korean peninsula that, as in the past, is open to differing interpretations. In selling the outcome as a win, Trump also pointed to what appears to be Kim’s sole new concession, destruction of a “major missile-engine testing site.”2

Although Trump proclaimed on Twitter that his diplomatic engagement means “there is no longer a nuclear threat from North Korea,” Pyongyang has yet to dismantle a single warhead, ballistic missile, or launch site. Until that happens, the threat remains salient, even if bilateral tensions have eased.

Now that the public show is over, the difficult work toward nuclear disarmament begins. The most promising near-term option to build U.S.-North Korean confidence and make meaningful progress toward nuclear disarmament is to obtain Pyongyang’s signature on and ratification of the Comprehensive Test Ban Treaty (CTBT). If Kim is serious about turning back the clock on his nuclear program, permanent cessation of nuclear testing should be mutually agreeable. The treaty would restrict North Korean nuclear weapons development and lock the regime into arms control commitments. Further, it would open the door for representatives of the Comprehensive Test Ban Treaty Organization (CTBTO) to verify the recently declared closure of the nuclear test site at Punggye-ri.

Debating Disarmament

In fewer than seven years in power, Kim has achieved the dream of his father and grandfather by meeting with the sitting U.S. president as an equal. Yet, his willingness to verifiably eliminate his nuclear weapons remains suspect; North Korea had promised to denuclearize at least six times prior to the Singapore summit.3 Barring an unexpected overture from Kim, the Trump administration needs to lay out a series of concrete, feasible steps to kick-start the dismantlement of the North’s nuclear arsenal. These steps should provide policy specifics to implement the overall framework of the joint statement and move the process forward.

Much of the skepticism about postsummit prospects stems from contrasting U.S. and North Korean interpretations of nuclear disarmament. Prior to the Singapore meeting, the Trump administration said that North Korea must engage in complete, verifiable, irreversible dismantlement of its arsenal. This position is similar to the so-called Libya model, wherein U.S. technical experts collected former President Moammar Gaddafi’s nuclear program and transported the components to Oak Ridge National Laboratory in Tennessee. North Korean officials have shown no interest in this proposal, championed most vociferously by U.S. national security adviser John Bolton, which briefly led to the summit’s cancellation.4 The Pentagon and the CIA assess that Kim will not fully disarm in the immediate future.5

In the joint communiqué, North Korea “commits to work toward complete denuclearization” of the Korean peninsula. Similar wording appears in the Panmunjom Declaration, signed April 27 by Kim and South Korean President Moon Jae-in. This is the historic North Korean position dating back to the days of Kim Il Sung, the first leader of North Korea and Kim Jong Un’s grandfather.

The United States and its allies contend that “denuclearization” refers to the rollback of the North’s nuclear program, while Pyongyang’s leaders have long conditioned any backing away from their nuclear aspirations on an absence of external security threats. Previously, they have called for an end to the U.S. military alliance with South Korea, withdrawal of U.S. troops from the peninsula, removal of South Korea and Japan from the U.S. nuclear umbrella, and even U.S.-North Korean nuclear disarmament.6 Only time will tell if the United States and its allies can bridge the perception gap with North Korea and overcome the missed opportunities of past accords, notably the so-called Agreed Framework and the statements from the six-party talks.

At North Korea's Punggye-ri nuclear test site, international journalists stand near a tunnel entrance before its demolition May 24. No international experts were invited to verify the extent of the destruction of the tunnel network at the remote, mountainous site. (Photo: News1-Dong-A Ilbo via Getty Images)Consequently, building confidence with incremental, verifiable steps marks the best path on the long road to disarmament. Many critics are rightly suspicious of Kim’s willingness to disarm, but others have struck more cautious notes of optimism about a road map for eliminating the North’s nuclear program over the next decade or longer.7 The administration’s messaging about the timeline for doing so has been inconsistent, however, which suggests that the U.S. side does not have a clear plan to propose to North Korea. Secretary of State Mike Pompeo has indicated that disarmament could occur in as little as two years, but Trump has walked back expectations by saying, “It does take a long time to pull off complete denuclearization.”8

A number of other potential steps could initiate nuclear disarmament. Yet, each poses challenges that will take time to overcome. Some possibilities involve setting initial caps on the number of North Korean long-range missiles or nuclear warheads or demolition of ballistic missile launch sites. Kim declared his April freeze on weapons testing only after the regime had conducted six nuclear explosions and 117 ballistic missile flights that gave him sufficient confidence in the performance of his arsenal.

It appears highly unlikely that North Korea will agree to near-term limitations on systems that contribute to deterrence by creating mutual vulnerability with the United States.9 Establishing accurate stockpile numbers and determining that the regime is not hiding weapons also require verifiable fissile material accountancy and extensive interviews with North Korean technical experts. Given the potential effects of such disclosures on deterrence, this sort of concession will require a much stronger level of bilateral trust than currently exists.

Another option might be for inspectors from the United States and the International Atomic Energy Agency (IAEA) to access critical fuel-cycle facilities, such as those used for uranium enrichment and plutonium separation. Such facilities, however, are dispersed throughout North Korea, and understanding the scope of fuel cycle activities to negotiate a potential dismantlement plan will be a lengthy endeavor. In total, at least 141 known sites are associated with the North Korean nuclear weapons program, fuel cycle and otherwise.10 Granting inspectors access to all of these sites would be an unprecedented action for the highly secretive North Korean regime.

An Opening for the Test Ban

The verification hurdles suggest that even if Kim is committed to the process, North Korean nuclear disarmament will be slow and at times frustrating. Still, U.S. officials should not lose sight of the goalposts. Although few experts outside of the White House believe that Kim will part ways with any of his nuclear weapons soon, the CTBT presents a way to immediately freeze and begin rolling back the program.

The North Korean regime’s rhetoric in recent months suggests an opening for the test ban to play a central role at the outset. On April 20, Kim declared moratoriums on nuclear and ballistic missile tests and announced the permanent closure of the Punggye-ri test site. He stated, “Under the proven condition of complete nuclear weapons, we no longer need any nuclear tests…. [T]he nuclear test site in [the] northern area has completed its mission.”11 At the Conference on Disarmament in Geneva, North Korean Ambassador to the United Nations Han Tae Song strengthened the message, noting that his country “will join international disarmament efforts for a total ban on nuclear tests.”12

The only nonproliferation regime that comprehensively addresses all aspects of prohibiting nuclear explosive testing is the CTBT, and North Korea’s acceptance of the test ban would bring about the benefits listed below that should not be overlooked by negotiators.

Building confidence and probing Kim’s intentions. The CTBT offers a litmus test of Kim’s credibility and nonproliferation bona fides. On one hand, he appears assured in his ability to strike the United States with nuclear missiles and claims that explosive tests are no longer necessary. On the other hand, acceptance of a legally binding moratorium on testing should not be taken lightly because it would place significant constraints on North Korea’s nuclear weapons development.

North Korea has conducted six nuclear tests of increasing sophistication since 2006, and the last one, in September 2017, may have been a thermonuclear device, given explosive yield estimates of up to 280 kilotons.13 Still, six tests with just one potential hydrogen bomb explosion that may have actually been a boosted fission device is not a lot when it comes to weapons development. The United States conducted 1,030 tests before declaring a moratorium in 1992, and its first full-scale thermonuclear burn of 10.4 megatons took place in 1952 at Enewetak Atoll in the Marshall Islands. Russia and China have carried out 715 and 45 tests each, respectively.

Pyongyang would curtail its ability to make a number of technical advances in its nuclear arsenal by terminating its testing program. Specific developments that would become difficult, perhaps nearly impossible in some cases, include building thermonuclear weapons with much higher, possibly megaton yields; producing smaller, lighter, and more deliverable warheads; and deploying multiple independently targetable re-entry vehicles on ballistic missiles. The regime almost certainly lacks an infrastructure for high-performance computing simulations and laser fusion experiments. Even if it were to improbably gain such advanced capabilities, its small repository of explosive testing data would limit their utility for weapons development.14

Signing and ratifying the test ban would also provide insight into Kim’s intentions because it would lock the regime into treaty commitments. History shows that the international community harshly punishes states that join multilateral nuclear arms control treaties and then violate them, regardless of whether they withdraw before doing so. North Korea has never signed the CTBT, but had ratified the nuclear Nonproliferation Treaty (NPT) prior to its withdrawal in 2003. When North Korea carried out its first test at Punggye-ri three years later, despite being a nonmember of the NPT, the UN Security Council imposed biting sanctions under Resolution 1718. India and Pakistan have never joined the CTBT and NPT, but faced censure rather than sanctions in Resolution 1172 following their 1998 tests.15

Verifying the closure of Punggye-ri. Kim’s announcement that the Punggye-ri nuclear test site would be shuttered and destroyed in the lead-up to the Singapore summit was a positive development. There are legitimate reasons, however, to doubt the permanence of this action. Verification at the test site is necessary to demonstrate North Korea’s commitments to nuclear disarmament while showing the regime that it will be treated in a fair and transparent manner during the process. The CTBT could facilitate impartial international verification of the shutdown of Punggye-ri.

On May 24, as a group of about two dozen international journalists watched, North Korea carried out explosions for the alleged purpose of destroying the three intact horizontal nuclear testing tunnels at Punggye-ri. In the days before the demolition, the regime withdrew invitations for U.S. and South Korean technical experts to observe.16 The journalists present were not versed in the on-site and field inspection techniques needed to systematically analyze the day’s events. To add to these concerns, the press stood at an observation point just 500 meters away, raising questions about the size of the explosions and extent of what was actually destroyed. After the smoke cleared, satellite imagery showed that the tunnel entrances were razed, but the tunnels themselves may still be comfortably in place and recoverable with modest excavation.

Additionally, the test site’s command center appears to be operational, and the regime reportedly removed and relocated sensitive equipment before the blasts.17 Simply put, the closure of the test site requires verification; informal pledges from Kim are just not enough.

Establishing ties to the CTBTO. The CTBTO is the only international organization with the capabilities to verify that Punggye-ri is decommissioned and inoperable. CTBTO Executive Secretary Lassina Zerbo has offered the organization’s expertise in “site characterisation; site closure verification; post site closure and dismantlement verification; and online and remote monitoring.”18 Indeed, the CTBTO has a sizeable cadre of international inspectors and numerous other specialists through its Working Group B on verification issues, with expertise ranging from visual observation to overflight photography, environmental sampling, and drilling. Although official on-site inspections cannot occur until the treaty enters into force, the CTBTO stands ready to assist if Kim is legitimately interested in disarmament.

The CTBTO could verify closure of the test site and, as Zerbo has suggested, establish a baseline for monitoring Punggye-ri. Techniques that could be used include ground-penetrating radar and magnetic and gravitational field mapping to locate cavities or hidden underground testing infrastructure such as piping and diagnostic cabling. Multispectral imaging could allow identification of changes in the test site’s surface and subsurface geological features over time. The deployment of mobile gamma-radiation detection equipment and seismic arrays could provide local monitoring of normal background and potentially aberrant geophysical events. From there, video and remote monitoring of the site could occur, including continuous collection of International Monitoring System (IMS) data.19

Singapore Summit Statement

The following are key portions of the joint statement issued at the conclusion of the June 12 meeting between U.S. President Donald Trump and Kim Jong Un, leader of the Democratic People's Republic of Korea (DPRK).

President Trump and Chairman Kim Jong Un conducted a comprehensive, in-depth and sincere exchange of opinions on the issues related to the establishment of new US-DPRK relations and the building of a lasting and robust peace regime on the Korean Peninsula. President Trump committed to provide security guarantees to the DPRK, and Chairman Kim Jong Un reaffirmed his firm and unwavering commitment to complete denuclearization of the Korean Peninsula.

Convinced that the establishment of new US-DPRK relations will contribute to the peace and prosperity of the Korean Peninsula and of the world, and recognizing that mutual confidence building can promote the denuclearization of the Korean Peninsula, President Trump and Chairman Kim Jong Un state
the following:

  1. The United States and the DPRK commit to establish new US-DPRK relations in accordance with the desire of the peoples of the two countries for peace and prosperity.
  2. The United States and DPRK will join their efforts to build a lasting and stable peace regime on the Korean Peninsula.
  3. Reaffirming the April 27, 2018 Panmunjom Declaration, the DPRK commits to work toward complete denuclearization of the Korean Peninsula.
  4. The United States and the DPRK commit to recovering POW/MIA remains, including the immediate repatriation of those already identified.

Having acknowledged that the US-DPRK summit—the first in history—was an epochal event of great significance in overcoming decades of tensions and hostilities between the two countries and for the opening up of a new future, President Trump and Chairman Kim Jong Un commit to implement the stipulations in the joint statement fully and expeditiously.

The United States and the DPRK commit to hold follow-on negotiations, led by the US Secretary of State, Mike Pompeo, and a relevant high-level DPRK official, at the earliest possible date, to implement the outcomes of the US-DPRK summit.

President Donald J. Trump of the United States of America and Chairman Kim Jong Un of the State Affairs Commission of the Democratic People's Republic of Korea have committed to cooperate for the development of new US-DPRK relations and for the promotion of peace, prosperity, and the security of the Korean Peninsula and of the world.


CTBTO experts are no strangers to this work, as the international community has invested heavily in the build-out of impartial, science-based procedures for test site verification. The organization has administered inspector training at the former U.S. test site in Nevada and former Soviet test site in Semipalatinsk, Kazakhstan. CTBTO representatives also visited the closed French test site at Mururoa Atoll in French Polynesia. Furthermore, the CTBTO carried out successful, large-scale, simulated, on-site inspections in integrated field exercises in Kazakhstan in 2008 and Jordan in 2014.20

Still, some observers have raised concerns about the possible existence of a secret test site. Unlike the nuclear fuel cycle or stockpile storage, nuclear testing is a highly concentrated and expansive enterprise. In the age of satellite imagery supported by machine learning algorithms, it is unlikely that North Korea has constructed a second test site undetected by Western intelligence agencies and interested nongovernmental experts, which does not mean the possibility can be summarily dismissed out of hand.

Even in the improbable worst-case scenario, this hypothetical second test site would be unusable unless Kim desired a return to the hostile pre-Singapore climate. The CTBT monitoring system of seismic, infrasound, hydroacoustic, and radionuclide sensors is nearly 90 percent complete and successfully detected all six North Korean nuclear tests with a high degree of locational precision. North Korea is fairly aseismic, so detection of nuclear tests and discrimination between natural and artificial geophysical events is relatively straightforward.

A U.S. National Academy of Sciences report in 2012 by top U.S. technical experts also concluded that the IMS and individual national technical means would make it exceptionally difficult for even very advanced nuclear-armed states such as Russia to conduct militarily significant evasive testing without getting caught.21 There is no convincing evidence that any state, much less North Korea, could confidently employ cavity decoupling or mine masking of nuclear explosive tests.22

Seizing the Opportunity

By meeting with Trump, Kim has achieved something that was unthinkable just a few months ago. He has even received and accepted an invitation to visit the White House. Yet, many experts have well-justified and pervasive questions about the extent of Kim’s commitment to change.23

No one thinks North Korean nuclear disarmament will happen tomorrow, but now is the time to formalize the principles in the summit’s joint statement with concrete actions. There is simply no other way to gauge Kim’s intentions and build the confidence between longtime rivals that will be necessary to achieve verifiable nuclear disarmament. The nuclear test ban offers a path forward that should be feasible and mutually agreeable while providing the best prospects for preventing this rare diplomatic breakthrough from going to waste.

Persuading Kim to sign and ratify the CTBT would also be a domestic political victory for Trump. Imagine if the president convinced the only country to have tested nuclear weapons in the 21st century to embrace a treaty banning “all nuclear explosions on Earth whether for military or for peaceful purposes.” North Korea would join 183 signatory states and 166 ratifying states that have endorsed the global norm against nuclear explosive testing.

The most recent national public opinion survey on the test ban indicates that 65 percent of Americans support the United States ratifying the CTBT, with 20 percent undecided, and just 15 percent opposed. Among Trump’s core political base, 56 percent of Republicans support the motion, with 20 percent undecided, and only 24 percent opposed.24 If Americans so strongly favor forever ending U.S. nuclear tests, support for halting North Korean tests is probably close to universal. For a president with few if any bipartisan wins, getting Kim to commit to the CTBT might be a major political breakthrough.25

Trump has also stated, “The prize I want is victory for the world.”26 Putting a stop to Pyongyang’s testing once and for all would be a victory in itself. Even more importantly, getting Kim to accept legal, political, and technical constraints on his nuclear program would be an ideal launching point for future conversations about warhead and ballistic missile controls, dismantlement, and the regime eventually rejoining the NPT. Where the discussions start and end remains to be seen, but the Trump administration should begin planning straightaway to develop the framework more specifically from the summit’s joint statement.

Prompting North Korea to join the test ban is perhaps the quickest way to benchmark Kim’s openness toward disarmament, qualitatively freeze his arsenal, and begin meaningfully rolling back his nuclear weapons program. There has never been a better time to put to use the international community’s long-term investment in the CTBTO.


1. Susan Page, “Analysis: When Trump Met Kim, the Handshake Was More Historic Than the Words,” USA Today, June 12, 2018.

2. U.S. officials said the reference is to a missile-engine test facility at the Sohae Satellite Launching Ground, according to Reuters. North Korea has not publicly confirmed that Kim made such a commitment.

3.  Brian Barrett, “All the Times North Korea Promised to Denuclearize,” Wired, June 12, 2018.

4. Mira Rapp-Hooper, “The Singapore Summit’s Three Big Takeaways,” The Washington Post, June 12, 2018.

5.  Stephen Herzog, “A Way Forward With North Korea: The Comprehensive Nuclear-Test-Ban Treaty,” War on the Rocks, June 11, 2018,

6. Duyeon Kim, “The Inter-Korean Agreement and Pyongyang’s Offer to Trump,” Bulletin of the Atomic Scientists, March 8, 2018, For a forthcoming fictional account of the potentially catastrophic consequences of U.S. misunderstandings about North Korean interpretations of denuclearization, see Jeffrey Lewis, The 2020 Commission Report on the North Korean Nuclear Attacks Against the United States: A Speculative Novel (Boston: Houghton Mifflin Harcourt, 2018).

7. Siegfried S. Hecker, Robert L. Carlin, and Elliot A. Serbin, “A Technically-Informed Roadmap for North Korea’s Denuclearization” (presentation, May 28, 2018),

8. Louis Nelson, “Pompeo: U.S. Will Seek ‘Major Disarmament’ From North Korea Over Next Two Years,” Politico, June 13, 2018; David Nakamura et al., “Trump-Kim Summit: Trump Says After Historic Meeting, ‘We Have Developed a Very Special Bond,’” The Washington Post, June 12, 2018.

9. Mark S. Bell and Julia Macdonald, “Toward Deterrence: The Upside of the Trump-Kim Summit,” War on the Rocks, June 15, 2018,

10. William J. Broad, David E. Sanger, and Troy Griggs, “The Nine Steps Really Required to Disarm North Korea,” The New York Times, June 11, 2018.

11. Joe Tacopino, “North Korea Announces It Will Suspend Nuclear, Missile Tests,” New York Post, April 20, 2018.

12. “Satellite Photo Offers Clue as N. Korea Promises ‘Total Ban’ on Nuclear Tests,” Associated Press, May 16, 2018.

13. Michelle Ye Hee Lee, “North Korea Nuclear Test May Have Been Twice as Strong as First Thought,” The Washington Post, September 13, 2017.

14. Herzog, “A Way Forward With North Korea.”

15. Ibid.

16. Adam Rawnsley, “Satellite Images Show North Korea Scrubbed Nuclear Test Site Before Unilaterally Destroying It,” The Daily Beast, May 30, 2018,

17. Ibid.; Frank V. Pabian, Joseph S. Bermudez Jr., and Jack Liu, “The Punggye-ri Nuclear Test Site Destroyed: A Good Start but New Questions Raised About Irreversibility,” 38 North, May 31, 2018,

18. Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization, “Statement by Lassina Zerbo, Executive Secretary, CTBTO, on the Singapore Summit,” June 12, 2018,

19. For an accessible discussion of the Comprehensive Test Ban Treaty’s monitoring and verification system, see Ola Dahlman et al., Detect and Deter: Can Countries Verify the Nuclear Test Ban? (New York: Springer, 2011), pp. 129-157. See also Andreas Persbo, “Compliance Science: The CTBT’s Global Verification System,” Nonproliferation Review, Vol. 23, Nos. 3-4 (2016): 317-328.

20. Oliver Meier, “Special Report: Major Exercise Tests CTBT On-site Inspections,” Arms Control Today, November 2008, pp. 32-38; Jenifer Mackby, “Special Report: Did Maridia Conduct a Nuclear Test Explosion? On-site Inspection and the CTBT,” Arms Control Today, January-February 2015, pp. 16-22.

21. Committee on Reviewing and Updating Technical Issues Related to the Comprehensive Nuclear Test Ban Treaty, National Research Council of the National Academies, The Comprehensive Nuclear Test Ban Treaty: Technical Issues for the United States (Washington, DC: National Academies Press, 2012).

22. Kaegan McGrath, “Verifiability, Reliability, and National Security: The Case for U.S. Ratification of the CTBT,” Nonproliferation Review, Vol. 16, No. 3 (2009): 412-414.

23. Vipin Narang and Ankit Panda, “North Korea Is a Nuclear Power. Get Used to It,” The New York Times, June 12, 2018; Jeffrey Lewis, “The Photo-Op Summit,” Foreign Policy, June 10, 2018,

24. Stephen Herzog and Jonathon Baron, “Public Support, Political Polarization, and the Nuclear-Test Ban: Evidence from a New U.S. National Survey,” Nonproliferation Review, Vol. 24, Nos. 3-4 (2017): 363-368.

25. Herzog, “A Way Forward With North Korea.”

26. Emily Cochrane, “President Trump a Nobel Laureate? It’s a Possibility,” The New York Times, May 9, 2018.

Stephen Herzog is a Ph.D. candidate in political science at Yale University and Nonresident WSD-Handa Fellow with the Pacific Forum of the Center for Strategic and International Studies. Previously, he directed a scientific engagement program supporting the Comprehensive Test Ban Treaty for the U.S. Department of Energy’s National Nuclear Security Administration.