[Trump's Second Term and Korea's Nuclear Option] I. Trump's Alliance Policy and the Future of Extended Deterrence

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I. Introduction: Changes in the International Order under Trump's Second Term

The re-emergence of President Trump signals significant changes to the liberal international order and alliance structures. The Trump administration's second term, advocating "America First 2.0," is expected to accelerate the restructuring of alliance networks and the redefinition of foreign relations. This is triggering the weakening of NATO and moves toward European self-reliance, as well as a decline in confidence in the nuclear umbrella among Asian allies. In particular, the ROK-U.S. alliance and extended deterrence cooperation are facing a critical inflection point.

The Trump administration has secured unprecedented policy-making momentum through institutional completeness and the appointment of loyalists, based on its victory in the 2024 presidential and congressional elections and the president's strong charisma. Armed with such immense power, President Trump, under the banner of "Make America Great Again" (MAGA), has been recalibrating foreign relations by rejecting international norms and institutions and eschewing free trade and alliance systems. Consequently, the post-war U.S.-led liberal international order is rapidly disintegrating, and U.S. allies may seek alternatives such as nuclear proliferation for their own security. This is because the U.S. has demonstrated a weakening of cooperation with traditional allies like NATO. In particular, the early termination of the Russia-Ukraine war, the redefinition of U.S.-Russia relations, and the pursuit of U.S. national interests through European self-strengthening are being observed as initiatives pursued with broad consensus within the Trump administration's second term.

However, critical perspectives argue that major U.S. decisions are made based on President Trump's impulsive judgments. In addition to shifts in the international security environment, President Trump's capricious personality and top-down policy-making style are accelerating uncertainty regarding U.S. policy priorities and the final outcomes of specific issues. If circumstances arise that negatively impact Trump's approval ratings due to strong backlash from countries like Canada, Mexico, and European nations, or a combination of stock market declines and economic deterioration within the U.S., predicting future developments will become even more challenging.

Another characteristic of Trump's foreign policy is its lack of overall strategic completeness despite its strong momentum. The Trump administration, at the national strategy level, identifies China as the primary threat, aiming to secure overwhelming superiority and win the strategic competition. However, the possibility of unexpected negotiations and deals, stemming from Trump's personal affinity for authoritarian leaders in Russia, China, and North Korea, constantly looms, further increasing international uncertainty. Notably, the full scope of the U.S. policy toward China has not yet been revealed. Once disclosed, it is expected that the U.S. will employ even stronger countermeasures in the fields of advanced technology and economic security than before.

Despite these Trump-related variables, the U.S. is expected to maintain its strategic emphasis on the Indo-Pacific strategy and strengthen its military readiness for potential conflict with China, in preparation for China's continuous military buildup. However, the strategy deviates from previous alliance strategies that sought integration with Europe to counter China, and there is insufficient explanation as to whether deterrence and containment of China can be achieved without European cooperation. This raises questions about whether the resulting natural alignment between Europe and China is truly beneficial to U.S. national interests or its ultimate victory in the strategic competition.

Meanwhile, President Trump is pursuing the strengthening of immigration barriers, including the mass deportation of undocumented immigrants, and imposing tariffs on countries with trade surpluses with the U.S. as a top national priority. For example, the U.S. is engaged in a fierce tariff war, imposing tariffs of up to 245% on Chinese exports to the U.S. The indiscriminate tariff offensive, regardless of alliance status, makes a realignment of alliances inevitable. Such indiscriminate tariff impositions will increase the burden on allies' security relations with the U.S. While the uncertainty surrounding the timing and grace period of tariff imposition may help the U.S. gain a tactical advantage to some extent, it appears to lack completeness as a foreign policy. In the long run, it could lead to a loss of overall U.S. national interest in winning the strategic competition by weakening bilateral relations with allies and partners and their multilateral ties. Ultimately, risks such as European cohesion, the rearmament of major European countries like Germany, the pursuit of a European nuclear umbrella, and heightened military competition and anxiety over extended deterrence among Asian allies are ever-present.

II. Trump's Second Term Alliance Policy and Extended Deterrence Discussions

1) Coexistence of Negative and Positive Views on Alliance Policy

The Trump administration's second term is accelerating the structural reorganization of alliances through a retreat from policies toward Europe and a differentiated approach to Asia. Some European countries are discussing the development of their own nuclear deterrence capabilities, which could lead to distrust in extended deterrence in Asia (negative view). Conversely, in the Indo-Pacific region, there is a possibility that extended deterrence will continue to be strengthened due to the need to maintain alliances to counter China (positive view).

First, the negative view posits that the U.S.'s anti-alliance policies toward its European allies will be applied without exception to the Korean Peninsula and East Asia. In other words, European countries are considering European nuclear sharing and independent nuclear armament, excluding the U.S., to fill the security vacuum created by the U.S. retreat, and this atmosphere is feared to spread globally. Since its inception, the Trump administration's second term has pursued overtly pro-Russian policies, unilaterally forcing Ukraine to cede territory disadvantageously and demanding the replacement of the Zelensky government to achieve an early end to the Russia-Ukraine war. By breaking promises made to Ukraine, a friendly nation, unlike the Biden administration, it has raised concerns that promises made to other friendly nations and allies could be revoked or altered at any time.

Ultimately, due to the U.S.'s adoption of anti-alliance policies, European countries have begun to consider receiving 'extended deterrence' from countries other than the U.S. for their own security (Rose 2025). Positive responses have emerged regarding the development of independent European deterrence (European Deterrent), particularly centered around countries like Germany, the UK, and France. Among these, a plan to build independent nuclear deterrence capabilities by sharing European nuclear weapons, led by leaders of nuclear-armed states such as the UK and France, has begun to be discussed.

However, even in this scenario, the ultimate authority to use European nuclear weapons would rest with the presidents of each nuclear-armed state, similar to U.S. extended deterrence. Therefore, just as NATO member states distrusted U.S. extended deterrence, there remains a possibility of distrusting the reliability of extended deterrence from the UK and France. Furthermore, the UK, a key country, faces two dilemmas regarding its nuclear deterrence capabilities, necessitating close cooperation with the U.S. First and foremost, the UK leases U.S. Trident missiles for cost-saving reasons, making the compatibility of its own nuclear warheads with U.S. missiles crucial, thus requiring close cooperation with the U.S. and exposing it to excessive dependence on the U.S. Additionally, the continuous delays in the UK's own Trident performance upgrades and the replacement of its next-generation ballistic missile submarines (SSBNs) are increasing concerns about a gap in nuclear deterrence capabilities.

In addition, there have been indications from countries such as Ukraine, Poland, and Germany about the possibility of considering independent nuclear armament, suggesting these nations might attempt to develop their own nuclear weapons for security. However, independent nuclear armament faces numerous hurdles, including securing nuclear materials and acquiring nuclear weapon manufacturing technology. It remains uncertain whether the U.S. would permit nuclear proliferation without imposing sanctions and tolerate the abandonment of the alliance system. Thus, some countries interpret Trump's potential withdrawal from NATO and pro-Russian stance as an abandonment of the European alliance system, leading them to seek alternatives disconnected from the U.S. regarding nuclear deterrence. However, the prevailing sentiment among most European countries is not to view Trump's demands as a withdrawal or dissolution of NATO, but rather as a call for European self-strengthening, which translates into increased defense budgets, higher burden-sharing, and expanded defense roles and contributions.

Ultimately, the heated atmosphere surrounding the nuclear deterrence vacuum in Europe was quickly diffused by the NATO Secretary General's firm statement, "There are no other means to replace the U.S. nuclear umbrella." However, the possibility of recurrence remains. For countries in the Indo-Pacific region, including South Korea, the spread of European independent deterrence efforts, coupled with increasing distrust in the U.S., will inevitably deal a significant blow to U.S. extended deterrence overall. In light of these changes, voices demanding independent nuclear armament are growing within South Korea, citing weakened confidence in U.S. commitments and Trump's lax policy stance on nuclear proliferation by allies.

In contrast to Europe, there is also a positive perspective that, although the Trump administration's second term pursues a differentiated alliance policy based on U.S. national interests, it prioritizes containing China. Therefore, it will strengthen extended deterrence guarantees and posture in close cooperation with allies in the Indo-Pacific region who require solidarity and support for this objective. This perspective focuses on the continuity and consistency of the military strategy aimed at China, which emphasizes strengthening military capabilities and posture, despite Trump's politically driven approach prioritizing economic interests. The strategic direction pursued by the Trump administration's second term appears to focus on the Indo-Pacific region over Europe, forming anti-hegemony coalitions, strengthening nuclear posture in the Indo-Pacific, modernizing the nuclear triad, and increasing low-yield tactical nuclear weapons.

For instance, Elbridge Colby, the Deputy Assistant Secretary of Defense for Strategy and Force Development, who is leading the development of the Trump administration's second term defense strategy, posited Taiwan and the South China Sea as critical conflict zones in his 2021 book "The Strategy of Denial," clearly outlining the roles of allies such as Japan, Australia, and South Korea in a limited conflict with China. Furthermore, in his testimony before the Senate Armed Services Committee on March 4, 2025, Colby responded to a question about the value of extended deterrence guarantees for Korean defense against North Korean and Chinese threats by stating, "The strategic posture for deterrence and defense to protect the interests of South Korea and the United States must be robust and reliable, requiring a clear-eyed view of the threats posed by North Korea and China, burden-sharing among allies, and the maintenance of optimal defense and strategic sustainability of the alliance." In essence, the U.S. is pursuing a differentiated policy between European and Asian allies with China in mind, and it is understood that the U.S., unwilling to relinquish hegemony under any circumstances, is unlikely to permit the dissolution of the alliance system or nuclear proliferation by allies that symbolizes or accelerates it.

III. Prospects for Extended Deterrence on the Korean Peninsula and Policy Tasks

1) Prospects for Extended Deterrence on the Korean Peninsula

Various challenges and opportunities are expected to interact in the context of extended deterrence on the Korean Peninsula. In particular, the three policy recommendations for "strengthening North Korea deterrence" presented in the 2024 Heritage Foundation report hold significant implications for gauging the direction of U.S. policy on extended deterrence toward the Korean Peninsula.

First, the U.S. must urgently support South Korea's deployment and enhancement of forces to repel North Korean ground attacks. Second, considering the practical limitations of U.S. conventional force support in the event of a contingency on the Korean Peninsula, it is recommended that the transfer of wartime operational control (OPCON) be pursued as early as possible to enable the ROK military to independently repel North Korean ground attacks. Third, the U.S. Department of Defense emphasized the need to deploy more expanded and diverse U.S. limited nuclear options, enhance nuclear coordination with South Korea, and deploy a stronger and more efficient theater missile defense system while strengthening U.S. homeland missile defense. Specifically, it was stated that if it becomes clear that North Korea can overwhelm or surpass U.S. homeland missile defense, other options should be evaluated to ensure reliable defense of South Korea and Japan, thereby deterring North Korea's use of nuclear weapons and WMDs against South Korea or Japan. Dr. Peters, who co-authored this report, further argued in a separate report released in March 2025 that forward deployment of low-yield, adversary-specific, theater-range non-strategic nuclear weapons is necessary to deter China, Russia, and North Korea, respectively (Peters & Glickman 2025). In other words, he emphasized the need for the redeployment of U.S. tactical nuclear weapons to the Korean Peninsula to deter North Korean nuclear capabilities.

Ultimately, the shift in U.S. military strategy centered on its China strategy is highly likely to necessitate changes in the roles and functions of the ROK-U.S. alliance and U.S. Forces Korea. Inevitably, the U.S. is likely to seek to augment, rather than reduce, its overall regional force deployment to enhance deterrence against China and improve its defense posture for Taiwan. In this regard, the U.S. may demand from South Korea an expansion of strategic flexibility for U.S. Forces Korea, guarantees of support in case of a Taiwan contingency, cooperation in the defense industry, cooperation in missile defense for U.S. homeland defense, increased defense spending, and expanded burden-sharing. Regarding extended deterrence, rather than demanding cost-sharing, the U.S. may instead seek discussions related to posture enhancement, such as forward deployment of forces and assets.

Specifically, as measures to strengthen strategic deterrence at the regional level, the U.S. is reportedly considering (1) regional deployment/enhancement of theater nuclear forces, (2) review of tactical nuclear redeployment to the Korean Peninsula, (3) forward deployment of MDTF (medium-range missiles), and (4) review of applying a NATO-like model. The U.S. may request consultations on the approach to these measures. The background to this U.S. approach is believed to be the need to prepare for simultaneous conflicts in East Asia and the perceived deterrence gap due to the relative shortage of theater nuclear forces.

2) Increased Possibility of Tactical Nuclear Redeployment

Given the escalating North Korean nuclear threat and the need to adjust the ROK-U.S. alliance, discussions on the redeployment of B-61 series tactical nuclear weapons to the Korean Peninsula are likely to intensify to alleviate concerns about the abandonment of U.S. extended deterrence. In this case, the establishment of storage facilities, operational systems, and strategic communication with the public and neighboring countries will be crucial.

The issue of redeploying tactical nuclear weapons to the Korean Peninsula is highly likely to emerge as the most contentious issue in the ROK-U.S. alliance going forward. Considering the scarcity of suitable tactical nuclear weapons (non-strategic nuclear weapons) for the U.S. to deploy to the Korean Peninsula, the most viable option for the shortest term would be B-61 series nuclear bombs deliverable by aircraft. To deploy these, storage facilities and dual-use aircraft certified for such missions must be in place beforehand. In other words, regardless of political and strategic considerations, physical preparations such as storage and maintenance facilities, operational personnel, and aircraft must be completed.

In addition, South Korea must be fully prepared for potential political and social controversy. Sensitive issues such as the redeployment of tactical nuclear weapons and the strategic flexibility of U.S. Forces Korea carry the potential for unproductive domestic debate and strong backlash from neighboring countries. Therefore, strategic communication plans and public communication strategies must be meticulously developed to prepare for potential backlash from neighboring countries like China, Russia, and North Korea. Of course, there is also a possibility that the ROK-U.S. alliance will adopt a "neither confirm nor deny" (NCND) approach, maintaining strict secrecy on related matters. Regardless, this issue undoubtedly requires closer consultation and cooperation between the ROK and the U.S. than any other matter.

IV. Conclusion: The Need to Redefine ROK-U.S. Extended Deterrence Cooperation

Security threats and uncertainties surrounding the Korean Peninsula are gradually intensifying due to potential changes in the U.S. defense posture in the region, military cooperation between North Korea and Russia, the North Korea-China-Russia alliance, the advancement of North Korea's nuclear capabilities, and the possibility of simultaneous contingencies in Taiwan and on the Korean Peninsula. Based on the discussions so far, the Trump administration's second term will prioritize containing China and strengthening its defense posture in the region. Consequently, South Korea is likely to face both unprecedented challenges and opportunities.

In particular, South Korea must address several tasks in this increasingly uncertain security environment. First, it must systematize ROK-U.S. extended deterrence cooperation and strike a balance between expanding the strategic flexibility of U.S. Forces Korea and strengthening the U.S.'s extended deterrence or deterrence against North Korea. Furthermore, active consultation and cooperation between South Korea and the U.S. must be sought on key issues such as the possibility of tactical nuclear redeployment, OPCON transfer, and alliance cost-sharing. Specifically, preparations must be made for the possibility that Trump, who emphasizes political achievements, may suddenly engage in U.S.-North Korea negotiations at any time, using combined defense posture elements such as joint exercises and strategic asset deployments as leverage. Lastly, while maintaining the ROK-U.S. alliance as its foundation, South Korea must proactively and assertively establish its defense posture and play a leading role in the defense of the Korean Peninsula. This necessitates efforts such as strengthening independent defense capabilities, developing advanced weapon systems, and expanding asymmetric capabilities (space, cyber, AI, robotics, etc.). Moreover, this presents an opportunity to resolve issues such as the dual command structure of the current combined defense system, excessive reliance on U.S. Forces Korea intelligence, insufficient theater operational planning capabilities, and the reorganization of the ROK military's upper command structure.■

V. References

Han Ji-ye and Kim Hyun-ye. 2025. “Handing North Korea over to the Alliance, Stated in U.S. Defense Strategy Guidelines.” *JoongAng Ilbo*, March 31.https://www.joongang.co.kr/article/25324783.

Creedon, Madelyn, et al. 2023. “America’s Strategic Posture: The Final Report of the Congressional Commission on the Strategic Posture of the United States.” Institute of Defense Analysis. October 27.https://www.ida.org/-/media/feature/publications/A/Am/Americas%20Strategic%20Posture/Strategic-Posture-Commission-Report.pdf

Coughlin, Con. 2025. “Delays in Trident renewal put our deterrent in peril.” *The Telegraph*. March 5.https://www.telegraph.co.uk/news/2025/03/05/delays-in-trident-renewal-deterrent-in-peril/

Colby, Elbridge. Translated by Oh Jun-hyuk. 2021. *The Strategy of Denial*. Seoul: Park Young Sa.

Dans, Paul and Groves, Steven, et al. 2023. “Mandate for Leadership: The Conservative Promise.” Project 2025. The Heritage Foundation.

Horton, Alex and Hannah Natanson. 2025. “Secret Pentagon memo on China, homeland has Heritage fingerprints.” *The Washington Post*. March 29.https://www.washingtonpost.com/national-security/2025/03/29/secret-pentagon-memo-hegseth-heritage-foundation-china/

Peters, Robert and Eli Glickman. 2025. “Forward Deployment of Non-Strategic Nuclear Weapons Is Needed to Deter Adversary Aggression.” The Heritage Foundation.

Rose, Gideon. 2025. “Get Ready for the Next Nuclear Age.” *Foreign Affairs*. March 8.https://www.foreignaffairs.com/united-states/nuclear-age-proliferation-trump-nato-gideon-rose

Secretary of Defense. 2025. “Memorandum Directing the Development of the 2025 National Defense Strategy.” May 2.https://media.defense.gov/2025/May/02/2003703230/-1/-1/1/MEMORANDUM-DIRECTING-THE-DEVELOPMENT-OF-THE-2025-NATIONAL-DEFENSE-STRATEGY.PDF

Velez-Green, Alexander and Robert Peters. 2024. “The Prioritization Imperative: A Strategy to Defend America’s Interests in a More Dangerous World.” The Heritage Foundation.

Yeo, Andrew and Hanna Foreman. 2025. “Is South Korea ready to define its role in a Taiwan Strait contingency?” The Brookings Institution.

■ Ham Hyung-pil, Senior Research Fellow, Korea Institute for Defense Analyses

■ Editor:Kim Chaerin, EAI Research Assistant

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