Japan and a Discretionary Superpower: Alliance Management in the Second Trump Administration
- May 13
- 11 min read
Prof. Jimbo Ken | Professor, Keio University
The return of Donald Trump to the White House has revived a familiar but unresolved question in Tokyo: not whether the United States remains powerful, but how, and under what conditions, it now chooses to exercise that power. Recent Japanese public opinion data underscore this distinction. A December 2025 nationwide survey by Genron NPO shows that while many Japanese remain aware of America’s vast economic and military capabilities, confidence in the United States as a reliable and predictable ally has eroded significantly. Fewer than one in five respondents now say they trust the United States as an ally, and more than 20 percent report that they lost trust after the launch of the second Trump administration, reflecting growing unease not about American capacity, but about American intent and discretion.
Against this backdrop, most Japanese do not interpret the second Trump administration simply as a precursor to U.S. retreat or isolationism. Rather, it is increasingly seen as the consolidation of a more selective, conditional, and domestically driven superpower—one willing to deploy overwhelming economic or military power when core interests are at stake, but reluctant to do so in the service of an abstract international order or automatic alliance commitments. For Japan, therefore, the central strategic challenge is no longer how to reassure itself of American strength per se, but how to assess and respond effectively to the reliability, predictability, and scope of U.S. engagement in an era in which American power remains abundant, yet its application is governed by sharper political discretion and transactional logic.
This shift has profound implications for Japan’s security strategy, particularly under the government of Prime Minister Takaichi Sanae, Japan’s first female prime minister, who assumed office in October 2025. For decades, Japan’s security policy had rested on a comparatively stable premise: that the Japan-U.S. alliance, as the cornerstone of national defense, would function on the assumption of American intervention. Accordingly, Tokyo focused on strengthening deterrence, enhancing its own capabilities, and reinforcing alliance coordination so that U.S. power could be mobilized decisively and in a timely manner in response to regional contingencies.
A central task for Japan, therefore, was to build and institutionalize alliance mechanisms that could translate American power into credible deterrence under changing regional and strategic conditions. These efforts included establishing and regularizing high-level coordination frameworks, such as the annual U.S.–Japan “2+2” meetings of foreign and defense ministers; revising the Guidelines for U.S.–Japan Defense Cooperation; and deepening bilateral and extended deterrence dialogues. Together, these mechanisms were designed to reduce ambiguity, align strategic expectations, and ensure that alliance commitments remained operational even as the distribution of power in Asia continued to evolve [1]. A core assumption underpinning Japan’s postwar security strategy is now being tested: the expectation that U.S. alliance commitments would translate into timely and decisive American intervention. U.S. capabilities across the military, technological, and economic domains remain formidable, but Washington’s approach to alliance engagement is evolving. Decisions regarding intervention are increasingly shaped by political judgment, assessments of national interest, risks of escalation, and domestic political sustainability.
For Japan, this evolution carries significant strategic consequences. Deterrence, crisis management, and defense planning must now account for scenarios in which U.S. involvement may be delayed, limited, or subject to greater political contingency. Alliance management is therefore no longer a matter of reinforcing assumptions, but of adapting operational expectations to an environment in which U.S. engagement cannot be treated as reflexive.
Within Japan’s policy and security community, the second Trump administration is widely understood as accelerating trends already visible during its first term: a preference for bilateral leverage over multilateral management, heightened sensitivity to domestic political constraints, and a growing emphasis on preserving presidential discretion in the use of power. The United States continues to invest heavily in military readiness, emerging technologies, and economic statecraft, but increasingly resists framing these capabilities as public goods for maintaining a liberal international order.
Credibility is sustained less by treaty language alone than by continuous coordination, visible burden-sharing, and alignment in peacetime as well as in crisis. Alliance management has therefore become more demanding, requiring sustained political and operational effort to ensure that formal commitments translate into effective deterrence under conditions of discretionary U.S. engagement.
The United States as a Discretionary Superpower
Recent debates in Japan increasingly center on the evolving logic that governs the exercise of American power. U.S. military, technological, and economic strength is widely treated as a given, while greater attention is paid to the principles, constraints, and decision-making processes that shape when and how that power is deployed. Comparable adjustments in U.S. alliance management have appeared in earlier periods— such as the Nixon Doctrine or debates during the Carter administration over U.S. force posture in Asia—when Washington encouraged regional partners to assume greater responsibility for their own defense. The current transformation, however, unfolds on a broader scale and is driven by a different combination of strategic, domestic, and systemic factors.
Three structural features stand out. First, Washington has narrowed its core interests, placing greater emphasis on homeland security, technological advantage, and the preservation of strategic flexibility rather than on the comprehensive stewardship of a rules-based international order. While competition with China remains a central reference point, it is no longer framed exclusively as sustained confrontation but increasingly as an arena in which rivalry, leverage, and selective engagement coexist. Second, the application of military and economic power has become more tightly coupled to domestic political calculations, reinforcing a preference for adaptability and presidential discretion. Third, alliances are no longer treated as standing guarantees, but as force multipliers whose value is continuously reassessed against cost, contribution, and strategic relevance. Together, these shifts underpin what many in Japan perceive as a discretionary superpower.
In the military domain, this reconfiguration is most visible in the evolving relationship between deterrence and alliance obligations. The United States continues to invest heavily in escalation- dominant capabilities and force modernization, underscoring its determination to retain military superiority. At the same time, however, the translation of these capabilities into automatic intervention on behalf of allies has become less certain. Decisions regarding intervention are increasingly concentrated at the presidential level, reflecting a preference for discretion over pre- commitment. This logic was exemplified by U.S. Secretary of Defense Pete Hegseth, who emphasized that the Department’s role is “to create and maintain decision space for President Trump, not to purport to make decisions on his behalf.”
Under Trump, deterrence is increasingly framed as a function of clearly defined national interests, manageable risks, and domestic political sustainability. This represents a significant departure from the assumptions that underpinned postwar U.S. alliances in Asia, where deterrence rested on the expectation that American intervention would follow once certain alliance thresholds were crossed. These thresholds traditionally included events such as an armed attack on allied territory, a large-scale conventional assault that threatened to alter the regional balance of power, or actions that directly challenged U.S. forward-deployed forces and treaty credibility [2]. In earlier alliance thinking, crossing such thresholds was widely assumed to trigger U.S. military involvement with limited political hesitation. Today, however, the link between threshold events and automatic intervention has become less direct, as decisions are increasingly filtered through assessments of escalation dynamics, alliance burden-sharing, and domestic constraints in Washington.
Beyond the military sphere, the transformation of American power is equally evident in technology and economic statecraft. Instruments such as export controls, investment screening, and industrial policy are increasingly deployed as tools of strategic leverage and bargaining, shaping alliance relations through concrete expectations and reciprocal contributions. In particular, under the Trump administration, allied cooperation was repeatedly linked to tangible economic and security commitments. Japan and South Korea were pressed to significantly increase defense spending, expand financial contributions for hosting U.S. Forces, invest billions of dollars in the U.S. economy, and accelerate the procurement of U.S. defense equipment.
This logic is reflected in recent leader-level engagements. At the October 2025 Japan–U.S. summit in Tokyo, the two governments announced a wide range of cooperative initiatives in areas such as economic security, critical minerals, advanced technology, and industrial collaboration. Many of these arrangements were structured as modular and non-binding, emphasizing flexibility and adaptability. From a Japanese perspective, this design underscores a central feature of the contemporary alliance: cooperation is deepening across domains, while the practical realization of commitments increasingly depends on ongoing coordination rather than on assumed reflexivity.
The Takaichi Administration and Domestic Configuration
If the erosion of automaticity defines the alliance environment Japan now faces, the question that follows is how Japan reorganizes its own political and institutional foundations to operate under those conditions. The Takaichi government emerged with an unusually energetic diplomatic opening. Shortly after taking office, Prime Minister Takaichi Sanae used major summits to secure rapid leader-level engagements, most notably with President Trump, as well as with South Korea and China. These early moves helped stabilize external relationships and signal continuity in Japan’s diplomatic posture.
More consequential, however, has been domestic political reconfiguration. The dissolution of the long-standing LDP–Komeito coalition and the formation of a new partnership with the Japan Innovation Party (Ishin) altered the center of gravity of security policymaking in ways that extend beyond parliamentary arithmetic.
For more than two decades, Komeito had functioned as a moderating force within Japanese security policy. Its role was not limited to coalition bargaining; it provided a structural brake on the pace and scope of reforms related to the use of force, defense exports, intelligence activities, and constitutional interpretation. This constraint contributed to political stability and coalition durability, but it also reinforced a policy style centered on incremental adjustment and risk avoidance—an approach well suited to an alliance environment premised on the assumption of reliable U.S. intervention.
The exit from this framework removed an important source of restraint, but it also exposed the governing coalition to new incentives. While a future realignment between the LDP and Komeito cannot be entirely ruled out, the current political configuration suggests that a simple return to the previous partnership is unlikely in the near term. The entry of Ishin as a coalition partner fundamentally altered these incentives. As a reform-oriented party seeking to demonstrate governing relevance at the national level, Ishin favored visible policy movement and executive decisiveness. As a result, the coalition realignment did not simply loosen constraints; it actively rewarded forward motion in defense and security policy.
This shift was operationalized through the LDP– Ishin policy agreement document, which functioned less as a general statement of shared principles than as a driver of concrete initiatives. Items that had previously faced political friction or procedural delay—accelerated revisions of strategic documents, expanded flexibility in defense equipment transfers, and reforms in intelligence and command-and-control frameworks—were placed at the center of the policy agenda. The agreement effectively translated coalition incentives into an actionable security program, lowering the political cost of reform and compressing decision timelines.
Prime Minister Takaichi’s own political thought reinforces this trajectory but does not fully explain it. Long before assuming office, she emphasized deterrence, sovereignty, and the visibility of national intent, arguing that strategic ambiguity invites miscalculation. Yet the Takaichi government should not be understood simply as the projection of a leader’s ideological preferences. The pace and direction of reform reflect an alignment between leadership beliefs, coalition incentives, and institutional opportunity. Security policy has thus become the axis around which the government’s governing identity is constructed— not only as a response to external threats, but as an adaptation to an alliance environment in which reliability can no longer be assumed, and domestic readiness carries greater strategic weight.
Strategic Signalling, Internal Balancing, and the Limits of Autonomy
The strategic challenge facing the Takaichi government is not simply how to signal resolve to an increasingly transactional ally, but how far Japan can strengthen its own strategic autonomy under conditions where U.S. intervention can no longer be presumed. In this context, strategic autonomy does not imply separation from the alliance or reduced integration with U.S. forces. Rather, it refers to Japan’s ability to sustain credible deterrence, command-and-control, and operational decision-making under scenarios in which U.S. involvement may be delayed, limited, or politically constrained. In an alliance environment defined by discretion rather than automaticity, signaling is inseparable from internal balancing. Measures such as increased defense spending, capability enhancement, and institutional reform are intended not only to reassure the United States but also to reduce Japan’s exposure to uncertainty by expanding the range of options it can credibly sustain on its own.
This logic is evident in how Japan interprets renewed U.S. pressure on defense expenditures. Calls for increased defense spending are understood less as coercive demands than as indicators of alliance relevance within a discretionary framework. From Tokyo’s perspective, higher defense investment serves a dual purpose: it signals seriousness and alignment to Washington, while simultaneously strengthening Japan’s capacity to operate in scenarios where U.S. engagement may be delayed, limited, or conditional. Strategic signaling, in this sense, is no longer merely communicative; it is increasingly embedded in material and institutional choices that shape Japan’s ability to bear greater responsibility.
Yet internal balancing alone has clear limits. Japan’s strategic autonomy remains constrained by geography, resources, and escalation dynamics, particularly in contingencies involving China or the Korean Peninsula. As a result, Japan has continued to invest in regional cooperation as a supplementary stabilizer. During the Biden administration, the pursuit of a “latticework” security architecture sought to thicken deterrence through interlocking mini-lateral partnerships. This approach was not designed to replace U.S. leadership, but to operationalize it more efficiently—by distributing burdens, increasing interoperability, and reducing the marginal cost of U.S. engagement.
Under the second Trump administration, however, the assumptions underpinning this approach have significantly muted. Minilateralism is most effective when underwritten by a credible U.S. commitment, because U.S. presence provides escalation management, high-end capabilities, and a focal point for coordination. Without that anchor, regional frameworks risk becoming consultative rather than operational, enhancing dialogue but falling short of meaningful deterrence. For Japan, this creates a structural dilemma: the more uncertain the U.S. commitment becomes, the more necessary regional cooperation appears, yet the same uncertainty also limits its effectiveness.
Proposals for deeper institutionalization, including ideas such as a Pacific Defense Pact, reflect an awareness of this dilemma. Such frameworks may promise greater predictability and shared expectations among like-minded partners. Yet under a presidency that prioritizes flexibility and unilateral actions, significant U.S. institutional commitments are unlikely. Moreover, divergent threat perceptions, capabilities, and political constraints among regional partners further complicate the feasibility of formalized collective defense arrangements in the Indo- Pacific. Institutional innovation may help at the margins, but it cannot resolve the fundamental challenge posed by a discretionary superpower.
In the end, Japan’s pursuit of strategic autonomy—whether through internal balancing or regional minilateralism—cannot escape its dependence on U.S. choices. This dependence is not simply a matter of habit or political preference; it reflects the absence of a viable strategic alternative. For Japan, there is no realistic “Plan-B” that can substitute for the U.S. alliance without incurring prohibitive strategic, political, and escalation costs. Geography, force structure, and the regional balance of power severely constrain the feasibility of autonomous defense or alternative security alignments at scale.
The task, therefore, is to shape an environment in which American commitment is exercised in ways that enhance and protect vital Japanese security and defense interests. In practical terms, this involves raising the strategic value of the alliance while reducing the political and operational costs of U.S. engagement, through measures such as increased Japanese defense spending, expanded operational roles for the Self-Defense Forces, sustained host nation support for U.S. Forces Japan, and deeper interoperability and procurement cooperation.
Japan’s strategy is best understood as an effort to increase the credibility and plausibility of U.S. engagement under conditions where intervention is no longer automatic. Strategic maturity, in this sense, lies in managing dependence rather than escaping it—by aligning domestic readiness, regional cooperation, and alliance signaling with the realities of a discretionary superpower.
Conclusion: Strategic Maturity Under Uncertainty
Japan’s challenge today centers on uncertainty over how and when American power is exercised. For Tokyo, the U.S.–Japan alliance remains indispensable as the core framework of Japan’s security, while its practical operation increasingly depends on political judgment and strategic conditions. For the Takaichi government, alliance reliability is therefore sustained through preparedness, credibility, and sustained alignment, rather than through assumptions about reflexive execution.
Japan’s options for strategic substitution remain sharply constrained. Enhanced self-reliance and regional cooperation contribute to resilience, but they cannot replicate the alliance’s deterrent and escalation-management functions without introducing significant risk. Japan’s strategic task is to shape the conditions under which U.S. commitment is most likely to be operationalized. These conditions include credible Japanese military capabilities, sustained host-nation support, high levels of interoperability and operational readiness with U.S. forces, and shared understanding of the strategic stakes surrounding potential contingencies.
Strategic maturity, in this sense, refers to the capacity to operate effectively under constraint: anticipating U.S. decision-making, reducing uncertainty for allied planners, and aligning domestic capabilities with alliance-sensitive signaling. In a security environment characterized by discretion rather than predictability, Japan’s effectiveness will depend on disciplined adaptation within an alliance that remains indispensable in value and conditional in execution.
Notes
[1]: For Japanese strategists, this transformation alters the grammar of alliance politics itself. Alliance reliability can no longer be treated as a fixed constant; it has become a variable that must be actively managed through coherent, consistent, and sustained engagement with the United States. The U.S.–Japan Security Treaty, including Article 5, remains firmly in place as the legal foundation of the alliance, but its deterrent effect depends increasingly on how commitments are interpreted and operationalized in practice.
[2]: Michael J. Green, By More Than Providence: Grand Strategy and American Power in the Asia Pacific Since 1783 (Columbia University Press, 2017).
About the Author
Prof. Jimbo Ken
Professor, Keio University
Prof. JIMBO Ken is a Professor of International Relations at Keio University and a Managing Director of Programs at the International House of Japan (IHJ/I- House). He is concurrently an adjunct Senior Research Fellow at the Canon Institute for Global Studies (CIGS). He served as a Special Advisor to the Minister of Defense, Japan Ministry of Defense (2020) and Senior Advisor to the National Security Secretariat (2018-20).
