Originally published by Pacific Forum, this article is republished with permission.
When US Under Secretary of War for Policy Elbridge Colby addressed the Strategic Command Deterrence Symposium on August 5, he described an effort to provide the president with more “sensible nuclear options,” including greater emphasis on low-yield nuclear capabilities for regional contingencies.
While Colby’s remarks had China and Russia in mind, he sparked a specific question in South Korea: Does this mean American tactical nuclear weapons could return to the Korean Peninsula?
A new South Korean opinion survey suggests that the public is also asking a more fundamental question about the credibility of US extended deterrence.
A different nuclear environment
The United States deployed nuclear weapons in South Korea from 1958 to 1991, with the number reaching approximately 950 warheads during its peak. Their withdrawal came as part of President George H.W. Bush’s global Presidential Nuclear Initiatives, instead of a Korea-specific assessment that the nuclear threat on the peninsula had disappeared. The decision was also intended to create diplomatic space with North Korea.
Seoul subsequently adopted the 1991 Declaration on the Denuclearization of the Korean Peninsula, and North and South Korea reaffirmed that principle in their 1992 joint declaration.
However, North Korea has conducted six nuclear tests, developed increasingly sophisticated delivery systems and adopted nuclear doctrine allowing preemptive and, under some circumstances, automatic nuclear use.
Pyongyang has also abandoned its longstanding characterization of relations with South Korea as a temporary division within one nation and now defines the South as a hostile separate state.
Therefore, the security environment that justified South Korea’s nonnuclear posture in the early 1990s no longer exists. Yet much of the institutional framework surrounding extended deterrence remains built around assumptions made more than three decades ago.
What South Koreans worry about
An August 11 survey by the Reform Institute, the think tank and policy research arm of the Reform Party, found that 75.1% of respondents supported the general proposition of redeploying US tactical nuclear weapons to South Korea.
Support was particularly high among younger respondents: 88.4% among those in their 20s and 86.3% among those in their 30s. This suggests that concerns about nuclear deterrence are not confined to older or traditionally conservative voters.
But another question complicates the picture. Asked to identify the single highest priority for addressing the North Korean nuclear threat, 36.3% chose strengthening the US nuclear umbrella and South Korea’s missile defense capabilities.
That exceeded support for developing an indigenous nuclear capability (26.9%), redeploying US tactical nuclear weapons (16.9%), or pursuing diplomacy and dialogue with North Korea (16.8%).
The distinction is important. South Koreans may be increasingly open to nuclear options, but a plurality still prefer strengthening deterrence through the alliance rather than pursuing an independent nuclear arsenal.
A third finding goes directly to the credibility of that alliance. Asked whether the United States would actually retaliate with nuclear weapons if North Korea used a nuclear weapon against South Korea, even if doing so exposed the American homeland to North Korean nuclear retaliation, respondents were almost evenly divided. 41.8% of respondents believed Washington would do so, while 41.7% did not.
This is the central problem for extended deterrence. Many Koreans appear uncertain whether threatening strategic nuclear retaliation remains credible when North Korea can retaliate against American cities.
The US Defense Department’s 2018 Nuclear Posture Review identified the risk that an adversary might believe it could conduct limited nuclear use without triggering a credible American response. Lower-yield and more flexible nuclear options were intended in part to close that gap.
South Koreans are now asking essentially the same question about North Korea.
More options require more consultation
As the survey shows, South Koreans recognize a gap in tailored deterrence against North Korea’s nuclear threat, while still showing greater willingness to rely on US extended deterrence than on an indigenous nuclear weapons program.
Seoul and Washington should reconsider the range of nuclear options. The answer need not be the return of US tactical nuclear weapons to the peninsula, but neither government should treat the question as permanently settled by decisions made in 1991.
In fact, physical redeployment of tactical nuclear weapons to the peninsula remains unlikely in the near term. Washington already possesses the W76-2 low-yield submarine-launched ballistic missile warhead and is developing the nuclear-armed sea-launched cruise missile, or SLCM-N. These capabilities can provide regional nuclear options without permanently stationing nuclear weapons on South Korean or Japanese territory.
That has obvious operational advantages. Nevertheless, it also creates a political problem for the alliance. A NATO-style model involving dual-capable aircraft and forward-deployed nuclear weapons requires host-nation infrastructure and extensive cooperation with the ally. Sea-based nuclear weapons require neither. But the fact that South Korea may not host the weapon does not mean Seoul has less at stake in how it would be used.
This makes consultation increasingly important as Washington reviews its nuclear employment guidance. Unlike a Nuclear Posture Review, employment guidance is classified and directly shapes nuclear planning. South Korea will not participate in the process in the same manner as the Nuclear Posture Review’s ally consultation process, nor will Seoul see the final document.
The two governments already created an institution designed to address precisely this problem. The US-ROK Nuclear Consultative Group (NCG) was established to deepen South Korean participation in discussions over nuclear deterrence and planning.
If Washington is now reconsidering the nuclear options that could be used in defense of South Korea, the NCG cannot simply become a mechanism through which Seoul is informed after the major decisions have already been made. South Korea does not need access to American nuclear operational plans. But it does need meaningful consultation on changes that directly affect the credibility and structure of extended deterrence on the peninsula.
Deterrence also needs political durability
American policy toward lower-yield nuclear capabilities has shifted repeatedly with changes in presidential administrations. The sea-launched nuclear cruise missile was revived during the first Trump administration, targeted for cancellation by the Biden administration following its 2022 Nuclear Posture Review, and sustained via congressional appropriation.
Yet, North Korea’s nuclear threats did not disappear during these political transitions.
A nuclear capability meant to strengthen extended deterrence cannot be fully credible if allies expect it to disappear every time politics change in Washington. Whatever posture the United States ultimately adopts in Northeast Asia needs broader bipartisan support, and so does South Korea’s own approach.
Nuclear policy has increasingly become a partisan wedge in Seoul, with calls for indigenous armament, tactical redeployment, and continued reliance on the existing framework dividing along political lines. A credible long-term strategy cannot change significantly after every election, in either capital. South Korean policymakers asking Washington for greater consistency should work toward the same at home.
Colby’s remarks have reopened an important debate: not simply whether tactical nuclear weapons should return to South Korea, but how the alliance adapts to a North Korea fundamentally different from the one it faced in 1991.
Whatever Washington and Seoul ultimately decide, if the United States is expanding the nuclear options available to its president South Korea needs a meaningful seat at the table as those options are considered.
Jun-seok Lee is a member of the National Assembly of the Republic of Korea and leader of the Reform Party. He previously served as the youngest-ever leader of the ruling People Power Party and was a 2025 presidential candidate. As a member of the ROK-US Congressional Caucus, he is a frequent contributor to bilateral policy discourse. Donghyeon Kim (donghyeon.kim@reformparty.kr) is a national security advisor to the Republic of Korea’s National Assemblyman Jun-seok Lee.
