How a Second Trump Term Could Shape the South Korea-U.S. Alliance

As the 2024 U.S. presidential election draws closer, U.S. allies and adversaries alike are preparing for the potential return of former president Donald Trump to the White House. Trump, having clinched the Republican presidential nomination, seems to have a significant chance of regaining the presidency given current President Joe Biden’s approval ratings have fallen below 40 percent. 

With an often unorthodox approach to foreign policy, a second Trump term could result in considerable geopolitical changes around the world. One relationship in particular that could be affected is the United States’ alliance with South Korea. Trump’s return to the Oval Office in 2025 would likely create friction in the South Korea-U.S. relationship in at least three distinct ways. 

First, Trump might break with South Korean President Yoon Suk-yeol on policy toward North Korea’s nuclear program. Yoon has so far pursued containment toward North Korea. He has sought to strengthen deterrence against North Korean aggression by deepening South Korea’s alliance with the United States. Similarly, Yoon has worked to bolster South Korea’s three-axis system, including missile defenses and retaliatory strike capabilities. 

At the same time, Yoon has tried to pressure North Korea into making concessions on its nuclear program by isolating the Kim regime economically and diplomatically. Yoon has emphasized that direct diplomacy with North Korea itself would only be worthwhile if it resulted in concrete progress toward denuclearization. Similarly, he has clarified that he will only support sanctions relief or economic aid to North Korea in exchange for verifiable steps toward denuclearization.

A second-term Trump might pursue alternatives to Yoon’s approach. In particular, Trump might be more open to engagement and accommodation toward Pyongyang than Yoon is. During his time in office, Trump favored personal diplomatic engagement with North Korean leader Kim Jon Un rather than seeking to isolate him. Trump met repeatedly with Kim for summits in Singapore, Vietnam, and along the Korean DMZ during his first term and claims to have remained in contact with Kim even after the end of his term in office. 

Trump suspended high-profile allied military exercises on the peninsula as part of his diplomatic outreach toward Kim, despite concerns that doing so might affect deterrence credibility. Since leaving office, he has continued to argue that these drills are provocative, implying they should be scaled down. 

Finally, Trump might diverge with Yoon on the question of sanctions. Rumors emerged in 2023 that Trump was contemplating offering sanctions relief to North Korea in exchange for a freeze on its nuclear program, rather than demanding progress toward denuclearization.

Second, Yoon and Trump would likely clash over the question of host-nation support for U.S. forces stationed in South Korean territory. While in office, the Trump administration demanded that South Korea increase its financial support for U.S. forces in Korea by 400 percent. This figure caused considerable tension in the allies’ relationship. Since leaving office, Trump has continued to emphasize the issue both on social media and in a recent interview with Time magazine.

Yoon has been supportive of a stronger South Korea-U.S. alliance and has expressed a willingness to shoulder more of a burden for the alliances’ common defense. Nevertheless, he is unlikely to agree to an increase of this magnitude. Indeed, the Yoon administration seems to be trying to preempt this issue by negotiating a new cost-sharing arrangement with the Biden administration prior to the 2024 elections.

Third, the gap between South Korea and the United States over relations with China might widen under a Trump administration. Yoon has, so far, hedged his bets with respect to South Korea’s relationship with China. On the one hand, South Korea has bolstered security ties with the U.S. and Japan despite Chinese opposition. It has also been more critical of China’s assertive conduct in the East China Sea, Taiwan Strait, and the South China Sea, as well as China’s continued cooperation with North Korea. 

At the same time, Yoon has tried to maintain a positive relationship with China. Notably, South Korea’s recent Indo-Pacific Strategy labeled China a “key partner for achieving prosperity” rather than a competitor or challenger. He backed away from a campaign pledge to acquire and deploy more of the Terminal High-Altitude Area Defense (THAAD) missile defense systems that China staunchly opposes. Furthermore, Yoon has declined to reduce South Korean semiconductor exports to China despite pressure from the Biden administration. His administration is also actively pursuing the resumption of the once-annual China-Japan-South Korea trilateral summit. South Korea is set to host the next edition of the leaders’ meeting, now taking shape at the end of May.

A second-term Trump administration, meanwhile, could end up adopting a more hawkish approach to China than the Biden administration. Although the Biden administration has maintained Trump-era steel and aluminum tariffs, Trump has recently argued that he would go even further to reshape the U.S. relationship with China. Specifically, Trump has called for a 60 percent tariff on all Chinese products, a step that might pave the way toward decoupling the U.S. and Chinese economies. Trump has also suggested he would return to the goal of a 350-ship U.S. Navy, developing a larger and more capable fleet to counterbalance China’s growing naval power in the Pacific. 

Some of Trump’s top China advisers, including Steve Yates and Kiron Skinner, have been highly critical of the Biden administration’s attempts to bring about a “thaw” in relations with China and have also called for a more confrontational approach. These steps might ultimately lead to a greater gap between South Korean and U.S. policies toward China, which could create tension in the alliance partnership.

Each of these gaps in and of itself has the potential to create friction between the United States and South Korea should Trump regain the presidency; all three, taken together, could do considerable damage to the alliance. Nevertheless, the South Korea-U.S. relationship has the potential to remain strong despite this friction, particularly if both governments embrace pragmatism and seek opportunities for compromise. 

The Trump-era revisions to the Korea-U.S. Free Trade Agreement (KORUS) in 2018 show that this type of pragmatic compromise is feasible. Trump campaigned on a pledge to rework U.S. trade relationships and had criticized KORUS as a “deal that should’ve never been made.” Initially, the Trump administration planned to withdraw outright from the agreement, a move that might have badly strained South Korea-U.S. ties. Similarly, South Korea initially refused to negotiate an adjustment to the agreement. 

Nevertheless, Seoul and Washington both seem to have recognized that a trade dispute was not worth derailing their vital military partnership. Instead, both sides sought out a mutually acceptable compromise, negotiating a successful revision to the agreement in 2018. This pragmatic approach left both allies in a stronger position in their subsequent bargaining with North Korea over its nuclear program.

Finally, an incoming Trump administration might ultimately find that issues beyond the Korean Peninsula require the bulk of its time, attention, and resources. The wars in Ukraine and the Middle East have raised global tensions and present immediate challenges to U.S. interests. Trump has promised to work toward resolving both conflicts, an endeavor that would require tremendous effort and political capital. Given these challenges beyond the Korean Peninsula, we believe that a second-term Trump administration can not and should not expend too much time and effort on transformational diplomatic initiatives on the Korean Peninsula.

Jihoon Yu is a research fellow at the Korea Institute for Defense Analyses. His expertise includes the ROK-U.S. alliance, ROK-Europe security cooperation, inter-Korean relations, defense policy, and maritime security. He earned his MA in National Security Affairs from U.S. Naval Postgraduate School and his Ph.D. in Political Science from the Maxwell School of Syracuse University.