The US–Japan–South Korea Trilateral: Resilience under Trump 2.0

At this past year’s Munich Security Conference, US Vice President JD Vance delivered remarks that rattled European allies by questioning America’s commitment to NATO and European defense. Yet on the sidelines, Secretary of State Marco Rubio convened a very different meeting: a high-level trilateral with his Japanese and South Korean counterparts. The juxtaposition was striking. While Europe was left wondering whether Washington still has its back, in Asia the message was one of reassurance. But is that reassurance credible under President Donald Trump’s second term?

The US–Japan–South Korea Trilateral Security Cooperation (TSC) has existed in one form or another since the 1990s. Its purpose has been consistent: to coordinate policy toward North Korea, strengthen deterrence in Northeast Asia, and uphold a rules-based regional order. For Washington, the trilateral has served as a mechanism to bind together its two most important allies in Asia. For Seoul, participation has fluctuated in tandem with domestic politics. Progressives tended to see the arrangement as a strategic insurance policy, while conservatives embraced it as a necessity. Japan, meanwhile, has consistently viewed the trilateral as an investment in regional stability.

Under Joe Biden, the TSC arguably reached its high-water mark. A record number of consultations, more than 80 in two years, were held at all levels of government. The “Commitment to Consult” agreed at the Camp David Summit in August 2023 symbolized the institutionalization of the trilateral. Beyond North Korea, the three partners aligned on China policy, regional infrastructure, supply chain resilience, and emerging technologies. For a moment, the trilateral seemed poised to become Asia’s closest analogue to NATO.

President Biden treated the trilateral as part of a “latticework” of mini lateral coalitions—the Quad, AUKUS, IPEF that collectively strengthened America’s Indo-Pacific posture. The emphasis was on institutional depth, long-term coordination, and integration across security and non-security domains.

Trump, by contrast, has long viewed alliances as dependencies to be leveraged. During his first term he demanded higher cost-sharing from both Japan and South Korea, questioned the value of US troop deployments, and entered into direct summit diplomacy with North Korea’s Kim Jong Un. That move effectively de-hyphenated Pyongyang from the trilateral framework and sidelined allies in favor of Trump’s personal brand of dealmaking.

Now in Trump 2.0, these instincts have not disappeared. The risk is that the trilateral could once again be reduced to a transactional bargaining chip rather than an institutional pillar of regional security.

The trilateral’s joint statements increasingly mention the Taiwan Strait, underlining its strategic importance. Both Tokyo and Seoul have come to recognize that cross-Strait stability is directly tied to their own security. Yet doubts remain over whether the United States under Trump would truly act if China moved militarily against Taiwan.

For America’s allies, the fear is not abstract. Trump has drawn a sharp line between the Euro-Atlantic and Indo-Pacific theaters, insisting they are unrelated, whereas both Japan and South Korea emphasize their connectivity. The nature of a peace settlement in Ukraine, they argue, will directly affect East Asia. Washington’s current posture under Trump suggests otherwise, feeding anxieties in Tokyo and Seoul.

This raises the possibility that the trilateral will have to serve as a hedge. If US commitment proves ambiguous, Japan and South Korea may be forced to deepen their own cooperation bilaterally and with other partners rather than rely on Washington alone.

The external environment in Northeast Asia is worsening. Russia, China, and North Korea are tightening military ties, coordinating more openly than at any time since the Cold War. This convergence makes trilateral cooperation not a luxury but a necessity.

There are ways to adapt the trilateral to Trump’s worldview. One option is to emphasize areas that align with his domestic priorities. Republican lawmakers have floated proposals to allow allied shipyards to build vessels or components for the US Navy and Coast Guard. Joint shipbuilding projects with Japan and South Korea could both address America’s naval shortfall and provide a concrete anchor for long-term cooperation.

At the same time, the risks of letting the trilateral atrophy must be made clear. A weakened TSC would signal disunity, embolden Beijing and Pyongyang, and undermine deterrence. Worse, it could push US allies toward alternative strategies: forging new mini-lateral groupings without Washington, accommodating Chinese demands, or even pursuing independent nuclear options. None of these outcomes would serve American interests.

The resilience of the trilateral under Trump 2.0 is not just an Asian question. It is a global one. If America’s closest allies in Northeast Asia cannot be certain of Washington’s commitment, then allies elsewhere including Israel must draw their own conclusions.

The lesson is clear: alliances are only as strong as their weakest link. Institutional frameworks like the US–Japan–South Korea trilateral matter precisely because they provide a buffer against political volatility in Washington. For Israel, which also depends on US support but faces regional instability, the imperative is to strengthen its own strategic partnerships, invest in autonomous capabilities, and track developments in Asia closely. The credibility of US commitments will increasingly be tested in the Indo-Pacific, and the results will reverberate far beyond the region.