The Peninsula

The Prospect for US-Korea-Japan Trilateralism in a Second Trump Administration

South Korean President Yoon Suk Yeol called to congratulate Donald Trump shortly after the US presidential election, telling the president-elect that the first Trump administration had set the foundation for US-Korea-Japan trilateral cooperation. Yoon later told the press he expected cooperation “would proceed well even during the [second] Trump administration.” Although some of the personnel that Trump has selected for key foreign policy and national security positions have been supportive of enhanced trilateral relations, it remains to be seen just how and to what degree the incoming Trump administration will build on the progress made in the trilateral relationship since the historic Camp David Summit, especially given Trump’s well-known agnosticism toward multilateral initiatives. Furthermore, given Yoon’s abortive martial law declaration, impeachment, and potential removal from office, his administration may well be replaced by a progressive successor less inclined to build upon Yoon’s efforts to strengthen ties with Japan and, by extension, US-Korea-Japan trilateralism.

Trump and US-Korea-Japan Trilateralism

Despite running a campaign that questioned the value of US alliances, the first Trump administration began working toward strengthening US relations with South Korea and Japan as early as 2017. During a trip to the region, which included stops in Seoul and Tokyo, President Trump said he “had the honor of sharing our vision for a free and open Indo-Pacific — a place where sovereign and independent nations…can all prosper side-by-side, and thrive in freedom and in peace.” His 2017 National Security Strategy emphasized the Indo-Pacific region, committing to “encourage the development of a strong defense network with our allies and partners” such as South Korea and Japan. In 2019, the Trump administration released its Free and Open Indo-Pacific strategy, adopting and advancing a regional concept that had been promoted by Japanese Prime Minister Abe Shinzo for much of the 2010s. Other states, including Korea and Japan, have released their own versions of an Indo-Pacific strategy. While President-elect Trump is known to quickly change his mind, these developments suggest it is unlikely he will reverse course on the Indo-Pacific, where South Korea and Japan are critical partners.

Although Trump has not yet been sworn into office, the contours of his national security and foreign policy team suggest his administration will support trilateralism. Senator Marco Rubio (R-FL) is expected to serve as the secretary of state and has strongly supported trilateral relations. When President Yoon and then Prime Minister Kishida Fumio visited Camp David in August 2023, the senator wrote on social media that a “trilateral alliance between the US, Japan, and Korea would be a crucial foundation that furthers our joint efforts in the Indo-Pacific.” Representative Mike Waltz (R-FL), who has been tapped as national security advisor, also seems to view the Indo-Pacific in a manner that supports trilateralism. Waltz, like Rubio, is one of the co-authors of an April 2024 congressional report on the need for a national maritime strategy. The document identifies China as a significant threat in this domain and calls for “mutually beneficial relationships with treaty allies, exploring comparative advantages to lower cost, time, and the complexity of rebuilding America’s domestic shipping and shipbuilding industry.”

Elbridge Colby, a member of the first Trump administration who has been tapped to be undersecretary of defense for policy, shares such concerns about China. Colby has been outspoken in identifying the Taiwan Strait and Korean Peninsula as potential conflict areas. He has stressed the need for South Korea to take on the overwhelming responsibility for its own defense (potentially including its own nuclear deterrent) and the interconnectivity between South Korean and Japanese security and promoted a rethinking of the US force posture on the Korean Peninsula and the broader Indo-Pacific region to more flexibly address simultaneous conflicts and threats from China. For his part, Pete Hegseth, former Fox and Friends Weekend host and Trump’s nominee for secretary of defense, has said little about the Indo-Pacific. However, his past news commentary on Fox News suggests he would be a vociferous supporter of Trump’s national security decisions, whatever they might be. Taken together, these prospective Trump administration officials suggest there will be voices supporting trilateral cooperation in dealing with security challenges in the Indo-Pacific.

Challenges for Trilateralism under Trump

However, ongoing political turmoil in South Korea following Yoon’s abortive martial law declaration and subsequent impeachment poses challenges to maintaining progress in trilateral relations. In the near term, South Korea’s interim leadership is hamstrung by its focus on stabilizing affairs and mitigating risks. As this drama plays out, South Korea may have limited bandwidth to focus on external issues like trilateral cooperation. Moving forward, if South Korea’s Constitutional Court upholds President Yoon’s impeachment, he may be replaced by his former rival and Democratic Party (DP) leader Lee Jae-myung, who leads in the polls. In a recent conversation with the Japanese ambassador to South Korea, Lee said managing relations with Japan and advancing US-Korea-Japan trilateral cooperation are “critical tasks.” Furthermore, Lee reportedly instructed fellow DP members to revise the National Assembly’s original impeachment resolution and remove language criticizing Yoon’s “Japan-centered foreign policy.” Yet, given Lee’s past comments critical of Japan, South Korea’s foreign policy would likely shift under his or another progressive leader’s administration.

While it is unlikely that Japanese Prime Minister Ishiba Shigeru will be removed from power in the near future, he faces an opposition-controlled lower house of the legislative National Diet and a contentious race to maintain control of the upper house this upcoming summer. This could pose obstacles for the government to pursue bold foreign policy moves to maintain stable relations with South Korea or strengthen the trilateral partnership.

That said, veterans of the first Trump administration are optimistic the president-elect will continue successful initiatives. “There’s a general concern, that I think is unfounded, that President Trump would abandon things that Joe Biden started and, you know, just abandon them because Joe Biden was involved in them,” said Alex Gray, a former Trump staffer on the National Security Council. However, that is not a given, and Korean and Japanese officials should identify how to give President-elect Trump a way to add his imprimatur to the trilateral relationship. “The value of trilateralism will need to be sold to him, not just grandfathered in,” said Dr. Jeffrey Hornung from the RAND Corporation. President-elect Trump may be open to furthering trilateral cooperation, but given his skepticism of existing institutions and initiatives, Seoul and Tokyo should underline the ways in which the relationship benefits Trump and his agenda.

Although it is still early, the officials expected to carry out Trump’s national security and foreign policy appear likely to continue the Biden administration’s efforts on trilateralism. A change in partisan leadership does not change some fundamentals about the Indo-Pacific region. North Korea remains threatening, China is still intractable, and the US bilateral alliances with South Korea and Japan maintain sizable support within both countries and among the American public. While things may change after Inauguration Day, hopefully, US-Korea-Japan trilateral cooperation will not be one of them.

Terrence Matsuo is a Non-Resident Fellow at the Korea Economic Institute of America. The views expressed here are the author’s alone.

Photo from Shutterstock.

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