▶️ Trump 2.0 and US-South Korea Relations: Donald Trump's re-election as US president introduces significant uncertainty for US-South Korea relations, with potential challenges such as renegotiation of the Special Measures Agreement, changes to KORUS Free Trade Agreement tariffs, troop withdrawals, and shifts in nuclear deterrence policies.

▶️ US-China Rivalry's Impact: The intensifying US-China rivalry under Trump's administration is expected to reshape the US-South Korea alliance, with possible demands for Seoul’s involvement in regional security, including a potential role in a China-Taiwan contingency, which could provoke tensions with China and North Korea.

▶️ Strategic Adjustments and Economic Implications: While potential tariffs and foreign policy unpredictability may strain relations, South Korea could leverage its strategic importance and investments in the US to mitigate risks, while benefiting from technological decoupling between the US and China in key industries like EV batteries and semiconductors.

Two monumental events have shaken US-South Korea relations over the last month: Trump’s re-election as US president, and South Korean president Yoon Suk Yeol’s attempted self-coup on the back of a martial law declaration. This article—which was commissioned prior to Yoon’s insane December 3 martial law decree, and has been modified accordingly—attempts to understand the former event in light of the uncertainty caused by the latter.

On November 5, Donald Trump was elected the 47th president of the United States of America, thus receiving a second term after his first mandate from 2017-2021. As he takes office in January 2025 with a new team of advisors and cabinet officials, Trump will certainly focus significantly on domestic and trade issues. Indeed, tax cuts, tariffs, government deregulation, energy policy, immigration enforcement, cultural issues (anti-DEI (Diversity, Equity, Inclusion) initiatives), and Trump’s lawfare vendetta against political opponents and the perceived “deep state” will demand a lot of Trump administration focus. Foreign, security, and defense policy will nonetheless receive significant attention, and South Korea will be a part of the mix.

Over the last year, much of the expert discourse regarding Seoul-Washington relations under Trump 2.0 has speculated on the incoming administration’s potential willingness to:

--force renegotiation of the SMA (Special Measures Agreement) or damage the KORUS Free Trade Agreement (including via tariffs),

--withdraw troops from the Korean Peninsula and/or otherwise undermine the US-South Korea alliance,

--weaken US extended nuclear deterrence for South Korea,

--neglect the blossoming US-South Korea-Japan trilateral relationship,

--allow South Korea to develop nuclear weapons,

--provoke crisis with North Korea, thus creating instability for South Korea,

--or negotiate an unfavorable deal (from South Korea’s perspective) with North Korea regarding Pyongyang’s nuclear arsenal.

Trump is notoriously unpredictable and unstudied, as well as typically “supported” by a chaotic cabinet and infighting officials and advisors, so there is a large potential variance in outcomes of Trump 2.0 foreign, security, and defense policy. This is true for policy concerning South Korea also. Nonetheless, all of the above areas are deserving attention, even if some (SMA renegotiation, tariffs) are more likely to occur than others (US troop withdrawal, unfavorable nuclear deal). And of course the aftermath of the self-coup attempt in South Korea will mean that the trilateral with Japan will be undermined, while the already low probability of US support for Seoul’s nuclear weapon development should be nearly nil. Indeed, the entire US-South Korea alliance dynamic will be dramatically altered if Yoon is forced from office and a typically US-lukewarm progressive president were to win a snap election.

However, there is one dynamic of the US-South Korea alliance that is almost certain to emerge during a second Trump administration, regardless of other factors: increasing pressure on the alliance due to sharpening US-China rivalry.

The new Trump administration—both in policy statements and presidential nominations for security/defense/foreign policy cabinet positions—has signaled that China will receive extraordinarily high priority from a group of hawks. Trump’s new national security advisor, Michael Waltz, as well as his deputy, Alex Wong, are known China hawks. The same holds for Marco Rubio and John Ratcliffe, the respective choices for secretary of state and director of the CIA. Pete Hegseth, the controversial and inexperienced selection for defense secretary (although he may not be confirmed), also has a reputation for a tough line on China.

It is probable that US allies and partners will be expected to join efforts to counter China. This could involve a range of actions, including military aspects of the US-South Korea alliance. Although previous US presidential administrations have taken small, quiet steps to begin this expansion of the focus of the US-South Korea alliance, Trump and his team will almost certainly push farther and faster. To wit, incoming NSA Waltz is on the record in a 2022 House of Representatives hearing demanding to know if South Korea would allow US forces stationed on the Korean Peninsula to be used in a Taiwan contingency. In this vein, the Trump administration may push for US Forces Korea to be postured more for a role in a regional (read: China-focused) conflict, rather than only for defense of South Korea. Trump may also press for US assets to be allowed to use airfields and ports on the Korean Peninsula as a part of US efforts to respond to a China-Taiwan conflict. The readouts of the 2024 US-South Korea Security Consultative Meeting and Korea-US Integrated Defense Dialogue included South Korean participation in regional force sustainment and MRO (maintenance, repair, overhaul), which, if utilized during a Taiwan contingency, would make South Korea party to the crisis.

Although there is increasing understanding in South Korea that its security is tied to regional developments, and that a China-Taiwan crisis would also implicate South Korean security, the aforementioned expansion and reconfiguration of US-South Korea alliance focus is deeply troubling to Seoul. In the first place, China would likely respond angrily. And although Beijing has been relatively muted in its irritation at increasingly close US-South Korea ties under Yoon and Biden, Washington-Seoul agreement that the alliance has a role in countering China would likely provoke a harsh response. Second, the prospect of US Forces Korea being flexibly postured to potentially contribute to the US response to a China-Taiwan crisis would raise the prospect of the US being distracted from its Korean Peninsula deterrence mission vis-à-vis North Korea, which might in turn opportunistically attack vulnerable areas such as those along the disputed Northern Limit Line.

Moreover, with Yoon likely soon to be out of office, and possibly a more pro-China progressive president serving instead, US and South Korean views on China may be less aligned. This adds an additional complicating variable to the situation.

Although less likely, another way in which US-China rivalry under Trump may affect the US-South Korea alliance is that Trump 2.0 may attempt to weaken China’s regional position via Washington’s interactions with Pyongyang. If the Trump administration were interested in isolating China, one option might be to drive wedges between Beijing and Pyongyang (China’s only de jure ally). It is unclear what it would take for such a deal to emerge—presumably both the US and North Korea would have to make sacrifices on priority issues in order to create a rapprochement sufficient to significantly weaken North Korea’s ties to China—but Trump is noted for his interest in attempting big, strategic alignment-inducing negotiations, including with dictators and other odious leaders. In the case of North Korea, such an attempt by the new Trump administration would likely implicate some form of de facto recognition of the Kim regime’s nuclear arsenal, which would greatly complicate South Korea’s security in the medium-/long-term, as well as upend decades of inter-Korean policy. It is unclear how a progressive South Korean president would deal with this situation, but in principle Seoul’s progressives support Washington’s diplomatic outreach to Pyongyang.

Although convoluted in its relation to China, Trump’s apparent desire to end the war in Ukraine may also affect the US-South Korea alliance. To wit, a primary strategic reason that Trump (and some senior officials) want to reduce support for Ukraine (and thus lead it to the negotiating table) is so that Washington can better focus on Beijing, which would have major indirect implications for North Korea, and thus for the US-South Korea alliance. Namely, North Korea is currently enjoying a splendid emergence from diplomatic and economic isolation (as well as from over-reliance on China) due to Pyongyang’s new alliance and strategic partnership with Moscow, which is providing North Korea with cash, food, energy, and military-technology support in exchange for artillery shells, short-range ballistic missiles, and troops. If the war in Ukraine were to end due to US pressure, this could dramatically reduce (from Moscow’s perspective) the need for Russia-North Korea cooperation, which would be a positive for South Korea. It might even lead North Korea to again return to more active diplomacy with the US and South Korea, which a progressive South Korean government would likely welcome.

Finally, even Trump’s much-feared potential tariffs are implicated in the dynamic in which US-China rivalry affects the US-South Korea alliance. That is, Trump’s “America First” tariff infatuation—both specifically vis-à-vis China, and more generally as directed to other states—stems substantially from a sense that hollowed-out US manufacturing jobs are the fault of China in particular and globalization in general, and thus tariffs are a measure for re-shoring manufacturing (and associated employment) to the US, while also hurting industry in China and other states competing with the US economically. Ignoring the general economic illiteracy of this view, which entails deadweight losses, at least for South Korea Trump’s tariffs might have a silver lining. In the first place, Trump is likely to prove flexible (transactional) on tariffs, and South Korea should be able to negotiate exemptions and other mitigating measures, based on its strategic importance and significantly increased investment into the US market. Second, in some areas—notably in emerging and high technology such as EV batteries and semiconductors—South Korea may end up being a relative winner in the long-term, as the US chokes off Chinese access to the cutting edge of these industries, which Beijing would otherwise acquire and develop at price points that would undercut South Korean competitiveness over time.

As mentioned, Trump 2.0 is likely to be unpredictable. Some of the above may happen, or all of it, or none. In any event, South Korea should be prepared for known knowns, known unknowns, and unknown unknowns.