By: Emma Chanlett-Avery, Duyeon Kim, and Yuka Koshino

Over the past two years, delegations to Washington from Japan and South Korea have one predominant question for their interlocutors: What would a Trump 2.0 administration mean for their countries and for U.S. global leadership more broadly? Both Asian capitals appreciate the upgrades to their bilateral pacts with the United States under the Biden administration’s alliance-centric foreign policy, and express anxiety about the possible return of Trump as commander-in-chief. Even before his election in 2016, Trump had expressed open disdain for U.S. alliances and that skepticism could be amplified in a second term by his “America First” approach.

With Kamala Harris now at the top of the Democratic ticket, Washington analysts assume broad continuity in her foreign policy approach, although nuances may yet emerge. But while a Harris election and a second Trump presidency contrast sharply on policy and style, the views from Seoul and Tokyo point to enduring elements of American foreign policy that are likely in either outcome.

In many ways, Trump and Harris share an approach to U.S. economic engagement in the Indo-Pacific. Upon taking office in 2017, Trump fractured the Obama administration’s core economic pillar of the so-called rebalance to Asia by withdrawing from the Trans-Pacific Partnership. This divorce drew dismay particularly from Japan; Tokyo had seen the 12-nation free trade pact as its primary tool to blunt China’s rising economic sway over the region and to reinforce its Free and Open Indo-Pacific strategy (FOIP). The Biden-Harris administration has similarly expressed little enthusiasm for re-joining the reformed version that Japan salvaged after the U.S. withdrawal, and its signature regional economic policy, the Indo-Pacific Economic Framework (IFEP) lacks the market access that the region’s economies crave. Japan and South Korea also had misgivings about the passage of domestic economic legislation such as the Inflation Reduction Act that would have penalized South Korean and Japanese investment in the United States. “Friend-shoring” rhetoric aside, both Seoul and Tokyo see either leader forging an industrial policy that defaults to protectionist trade practices.

Both Japan and South Korea are also concerned about diminishing American leadership of the world and the ascendance of illiberal, authoritarian blocs. Biden and the Democratic Party have generally promoted U.S. alliances as underpinning a world order that promotes stability and the rule of law. Yet during Biden’s presidency, wars in Europe and the Middle East have flared, threatening to distract Washington from its Indo-Pacific priorities and driving deep divisions in public opinion both domestically and internationally. Trump and his Republican colleagues, on the other hand, mostly disapprove of U.S. military involvement in international conflict and fidelity to international alliances, particularly NATO. A Trump administration could undermine the rules-based system by brokering deals with authoritarian leaders, neglecting multilateral institutions that seek to quell conflict, and reinforcing the rising ideological isolationism in U.S. politics.

Trump and Biden policy convergences aside, Seoul’s and Tokyo’s experiences with each president are starkly different. A Trump presidency would almost certainly present deeper challenges to each country and disrupt the web of security partnerships that both countries view as broadly stabilizing. How Trump would approach the China challenge is likely to be the central question: Will he be relatively supportive of U.S. alliances in the Indo-Pacific if he sees them as amplifying U.S. power and deterrence? Or will he seek to cut his own deals with Beijing that excludes allies’ interests? Would he demand multifold increases in the burden-sharing agreements supporting the U.S. military presence in the region that allies would resist?

A separate set of questions arises considering a Democratic victory. Would Harris opt to continue Biden’s approach to alliances? Would her administration see the Indo-Pacific as equally important to the trans-Atlantic partnership? Would Harris’s foreign policy team have a different view of how to handle strategic competition with China? All of these yet-unanswered questions loom large for Japan and South Korea over the coming months.

The View from Seoul

The conservative Yoon Suk Yeol government is confident that the alliance will remain strong regardless of who sits in the White House next year. Still, Seoul is expecting challenges with a Trump administration, and concerns and even anxiety can be felt in Seoul. On the other hand, Seoul appears more at ease about the prospects of working with a Harris administration because of policy familiarity and broad policy alignment as well as a degree of policy predictability.

South Korea’s experience with the Trump administration underwent many twists and turns. In 2017, relations had a rocky start when progressive South Korean President Moon Jae-in was elected because his views completely diverged from those of the Trump administration on how to deal with the Democratic People’s Republic of Korea (DPRK, or North Korea). Trump already had in place a “maximum pressure and engagement” strategy. South Korean progressives, on the other hand, preferred front-loading on concessions, although the Moon government achieved its goal of brokering U.S.-North Korea talks via inter-Korean engagement. Seoul and Washington eventually converged on each using summitry with Pyongyang as a method of diplomacy, but continued to disagree on detailed policy approaches. Eventually, the breakdown of the U.S.-DPRK Hanoi summit led to Pyongyang bullying South Korea and refusing to engage Seoul diplomatically for the remainder of Moon’s term; North Korea was apparently upset at the Moon government for raising false expectations about Hanoi and failing to convince Washington to lift sanctions against it. Trump’s demands for Seoul to pay more to host U.S. troops was another source of tension. Unable to reach an agreement, the burden-sharing pact expired, leaving thousands of South Korean employees furloughed and inflicting a major wound on the U.S.-Republic of Korea (ROK) alliance.

After President Biden took office in 2021, South Korea under Moon was reluctant to participate in global initiatives and contribute to strengthening the rules-based international order because of its domestic political aims and narrow focus on inter-Korean relations. The allies continued to diverge in their approaches to North Korea, China, and Japan.

Since 2022, however, the alliance was bolstered after conservative South Korean President Yoon Suk Yeol took office. Today, the allies are closely aligned in their approach towards North Korea, Japan, and China as well as upholding liberal democratic values at home and defending the rules-based international order. The allies have been working to strengthen deterrence against North Korea and reassure the South Korean public of Washington’s defense commitment. Seoul and Tokyo began to mend their relations, which have long been fraught with historical grievances and disputes, and held a historic trilateral summit with Washington at Camp David for the first time. Since then, trilateral cooperation quickly expanded and deepened across virtually all sectors of society.

The fate of trilateral cooperation may depend on the upcoming U.S. presidential election. If Harris is elected and if she continues to invest as the Biden administration has done in supporting trilateral cooperation, the three countries are expected to continue working together closely (barring any drastic changes in Japan’s or South Korea’s foreign polices after September 2024 and May 2027 respectively). If Trump is elected, the Yoon administration believes that the ongoing institutionalization of the three-country cooperation will keep the partnership intact. However, trilateral cooperation could stall, suffer, or even end, given both Trump’s treatment of allies and prior preference in foreign policy for bilateral mechanisms over multilateral ones.

On U.S.-South Korea relations, the allies are expected to continue on their current trajectory during a Harris administration. This means that the allies would also continue to work together intimately on regional and global issues. However, a possible area of contention could be the growing questions in Seoul on the reliability of U.S. extended deterrence. There is skepticism and anxiety in some South Korean circles about whether the alliance can deter a North Korean nuclear or conventional attack or sufficiently respond to one because of North Korea’s increasing nuclear weapon capabilities. Such skepticism and anxiety come from their perception that Washington is not doing enough to solve the nuclear problem, and many South Koreans do not feel reassured enough about America’s political commitment to defend their country. In addition, South Koreans are concerned about Washington’s attention span as it simultaneously grapples with two nuclear competitors, Russia and China, that are challenging America’s global leadership. All of these factors, in addition to Russia’s renewed mutual defense treaty with Pyongyang, have fueled calls among South Korean conservatives for South Korea the country to develop its own nuclear weapons.

Meanwhile, how Seoul would respond in a military contingency involving Taiwan and China remains unclear. While the Yoon administration has so far stood up to Beijing in clearer ways compared to its predecessors, Taiwan is still a very politically-sensitive topic in South Korea; factors at home and abroad would determine Seoul’s involvement in a military conflict. Seoul is also contemplating how to deal with Moscow in the wake of Russia’s latest pact with Pyongyang and alleged technical support for North Korea’s nuclear weapons development.

If Trump is elected, South Koreans will still have questions about Washington’s security guarantee. However, their insecurities will further spike if he treats allies in a transactional manner, strikes a deal with North Korea that threatens South Korea’s national security, and/or decides to withdraw or significantly reduce the number of U.S. soldiers in the country. The latter scenario will likely cause South Korea to embark on a path toward nuclearization. While President Yoon has reiterated his country’s commitment to the Nuclear Non-Proliferation Treaty and nuclear-weapons abstinence in the Washington Declaration last year, some in South Korean conservatives circles see a Trump victory to be their country’s opportunity and greenlight to go nuclear even if a Trump presidency damages the rest of the alliance relationship. Seoul will also continue to feel pressured to join Washington in decoupling from China and many South Koreans are concerned about Trump’s future trade policies potentially hurting their own economy. In these scenarios, frustration and even resentment would surface, but Seoul’s reaction to them would depend on circumstances in the alliance relationship and in the geo-economic/geo-strategic landscape.

The View from Tokyo

As it described in its historic National Security Strategy update in December 2022, Tokyo views today’s strategic environment as “severe and complex as it has ever been since the end of World War II.” This threat perception is driven by Russia’s aggression against Ukraine, rising tension in the Taiwan Strait, continuing nuclear and missile threats from North Korea, and deepening China-Russia strategic relations. In 2023, Hamas’s violent attack against Israel and the subsequent war in the Middle East and the Russia-North Korea partnership in defense and technological support are further adding turbulence to the environment.

Against this backdrop, Tokyo’s priority remains the strengthening of a rules-based free and open Indo-Pacific as a cornerstone of the broader international order. It has pursued its own robust security and defense transformation, an upgrade of the U.S.-Japan alliance, and increased cooperation with like-minded partners in Asia and beyond. No matter which presidential candidate wins in the November election, however, Washington’s ability and capacity to take on a regional and global leadership role is likely to be limited. Tokyo may need to pursue an even greater role to proactively shape the regional and international order.

The Trump presidency was defined by U.S. isolationism, unilateral and transactional approaches to foreign relations, and an economic policy that narrowly focused on addressing trade imbalances under the “America First” slogan. This approach was challenging for Tokyo as it sought to maintain the benefits and structure of the post-war U.S.-led liberal international order. In particular, the U.S. withdrawal from the Trans-Pacific Partnership (TPP, later the Comprehensive and Progressive Agreement for the Trans-Pacific Partnership, or CPTPP), which took nearly a decade to negotiate and was expected to have a strategic impact given its size and high standards, was a blow for Tokyo and triggered deep concerns about the U.S. commitment to the regional security and economic architecture. The administration’s ad-hoc and unpredictable diplomatic moves to strike a deal with North Korean leader Kim Jong-un were also troubling for Tokyo as the diplomatic strategy was conducted without a clear goal for the country’s denuclearization or for resolving abductee issues that remain politically salient in Japan.

Tokyo has demonstrated its ability to think innovatively as a rules-shaper, pursue proactive diplomacy, and showcase its ability to be a willing and capable partner for the United States. These approaches are all key to navigating the international environment under Trump 2.0. For instance, Tokyo championed free trade by concluding the signing of the CPTPP in 2018, simultaneously stepping up its defense and security commitments, and actively building a coalition among like-minded partners in the region and beyond to deal with the military and economic rise of China. The Abe government convinced Trump to adopt the FOIP policy early in his administration. With Tokyo’s encouragement, the Quadrilateral Security Dialogue (or “Quad,” comprised of Japan, the United States, Australia, and India) was revived in 2018 and expanded to include a geo-economic agenda. Coordination on economic security policy also advanced to reduce risks associated with Chinese digital high-tech. The 2020 Armitage-Nye report by the Center for Strategic and International Studies (CSIS) commended Tokyo’s role as an “idea innovator” and equal partner in the alliance and explained that Japan’s main policy drivers have shifted from “American gaiatsu (outside pressure) to Japanese leadership”.

In contrast, under the Biden-Harris administration, Tokyo does not necessarily need to be as “innovative.” Cooperation among U.S. allies and partners solidified through Biden’s leadership to enhance mini-lateral frameworks such as U.S.-Japan-Australia, U.S.-Japan-Philippines, and most importantly, the U.S.-Japan-ROK trilateral cooperation. Biden also elevated the Quad to the summit level in 2022 and made the framework more inclusive and acceptable to ASEAN countries. The U.S. and Japanese national security strategies released in 2022 respectively demonstrated deep alignment in their goals and approaches especially vis-à-vis China.

The Biden-Harris administration also required greater contributions from its individual allies. Accordingly, Tokyo maintained an active diplomatic posture, committed to fundamentally reinforcing its defense capability to take “primary responsibility” to defend itself, and to pursue further interoperability with the United States to enhance regional deterrence. With Washington’s hands full dealing with strategic fronts in Asia, Ukraine, and the Middle East. Tokyo will continue to implement defense and security transformation, including upgrading the alliance’s command-and-control framework and integrating the defense industrial and technological base.

In the economic realm, the Biden administration’s policies were largely a continuation of Trump’s “America First” protectionist policies. It is unclear if Harris will take a different path, but observers do not anticipate a major divergence. U.S. absence from the CPTPP, the lack of market access in the Indo-Pacific Economic Framework, continued opposition to the World Trade Organization (WTO) dispute settlement mechanism, and industrial policies emphasizing reshoring manufacturing to the United States as seen in the CHIPS Act and the Inflation Reduction Act all signal that Tokyo would need to bear a heavy burden of championing free trade.

However, Tokyo’s newly elected Prime Minister Ishiba Shigeru’s stated defense and security policies could pose a major risk to this pathway in two ways. One is the proposal to create “a collective self-defense system like NATO in Asia” to deter China as stated in his interview with Hudson Institute. Japan’s close partners, including India, are already expressing concerns to this transformative approach to regional security. Another is his determination to revise the U.S.-Japan Security Treaty and Status of Forces Agreement to seek “equal” partnership with the United States, such as stationing the Japan Self-Defense Force (JSDF) in Guam. These ideas are drastic shifts from the past three administrations, or even from the long-standing U.S.-Japan alliance system since the revised security treaty was signed in 1960, which could risk the stability of U.S.-Japan relations.

Policy Recommendations

For the U.S. alliances with South Korea and Japan to thrive — or merely survive — under the next administration, policy makers need to consider different options for different outcomes. Depending on the next president, the steps could be either defensive against U.S. unpredictability or reinforcing existing initiatives. With isolationism on the rise in the United States, it is essential in either outcome to build the ark now even if the next commander-in-chief is strongly supportive of U.S. alliances.

Both allies should continue to upgrade their own security capabilities, prepare for less or variable U.S support and to hold onto and defend any gains in interoperability as much as possible, whenever possible. The reality of this severe strategic environment is unlikely to change in the coming years. For Japan to enhance its domestic defense capability and convince Washington that it is an indispensable ally, Tokyo should endeavor to fulfill its political commitment to double domestic defense spending by the end of fiscal year 2027 and to remove legal and technical barriers to enhance interoperability not just among the armed forces, but among industries and defense innovation eco-systems to enhance joint deterrence and response capabilities. While the government has been increasing its investment pace, political instability and public resistance have delayed their decisions on raising taxes to fund the programs.

Seoul will similarly need to strengthen conventional military capabilities to demonstrate its own security investments and to deter DPRK aggression in preparation for the possibility of weakened U.S. extended deterrence. Seoul should not only robustly resource its own defense spending but also work to improve synergy among its services, strengthen cooperation in the Combined Forces Command (the U.S.-ROK joint warfighting command), and continue to advance large-scale bilateral — or mini-lateral — military exercises.

Reinforcing the web of security partnerships would deepen the “latticework” of the Indo-Pacific, hedging against the variability of U.S. leadership changes. The continuation of Seoul-Tokyo rapprochement is central to stabilizing the region. Absent American facilitation, the delicate balance of enhancing defense and economic cooperation and managing historical sensitivities is challenging, but both Japan and South Korea understand that the higher stakes of the security landscape reinforce mutual interests. The trilateral partnership born at Camp David could bear fruit as a stronger, more strategically aligned bilateral relationship. Other mini-laterals with Australia, the Philippines, NATO, and others should also continue if the United States pauses, downgrades or withdraws from these arrangements. The same approach should be applied in the geo-economic sphere, including continuing to press for a multilateral trade pactthat provides a counterweight to China-dominated arrangements and to make other trade agreements such as the Regional Comprehensive Economic Partnership (RCEP) and ASEAN free trade agreements as liberalizing and high-standard as possible.

Maintaining the global non-proliferation regime is another critical imperative. If U.S. extended deterrence is questioned, this will be a challenging task, particularly if North Korea continues to advance its nuclear weapon and missile capabilities. Reassurance to South Korea and Japan of U.S. commitment to its security guarantees — including under the nuclear umbrella — is a necessary, if not sufficient, factor to prevent the allies from developing their own nuclear arsenal. Seoul seems especially vulnerable to this development, but Japan could soon follow suit in a cascading breakout of a nuclear arms race.

If leadership in Washington appears unable or unwilling to maintain the strength of the two alliances, Seoul and Tokyo should seek other power centers in the United States in order to weather the storm of political turbulence. Developing stronger ties with the U.S. Congress could ensure more continuity at the official level, even if growing numbers of lawmakers appear hostile to alliances. Sub-national efforts to reach out to state and local leaders could also prevent the erosion of cooperation. Japanese and South Korean companies investing in the United States should also enhance their political and geo-economic literacy to avoid U.S. domestic political intervention in major economic deals. People-to-people exchanges and engagement with the grassroots can also help ameliorate the damage at the political level.

On its face, a Trump victory in November is likely to present significant policy challenges for both Seoul and Tokyo. But a Harris election holds some degree of political uncertainty as well, absent a more specific foreign policy blueprint that details continuity and changes from Biden’s approach. In either outcome, the allies must work to forge a future that does not solely revolve around Washington’s treaty commitments, but rather integrate those potentially diminishing guarantees into a broader, more comprehensive, and diversified security landscape.

Emma Chanlett-Avery is Deputy Director of the Asia Society Policy Institute's Washington, DC office and the Director for Political-Security Affairs.

Duyeon Kim is an Adjunct Senior Fellow with the Indo-Pacific Security Program at CNAS based in Seoul.

Yuka Koshino is an Associate Fellow at the International Institute for Strategic Studies and a doctoral student at the Keio University Graduate School of Law researching U.S. alliances and security, defense, and technology cooperation in the Indo-Pacific region.