The U.S.-South Korea relationship is about to enter a period of uncertainty. On Jan. 20, Donald Trump will be inaugurated — for a second time — as the 47th president of the United States. Judging by his first term, Trump's policy agenda and personal proclivities on international cooperation are likely to be misaligned with allies, including South Korea. On matters of trade, security and defense, diplomacy and the environment, the U.S. under Trump will pursue action to “make America great again,” action that may not be in the perceived interest of Seoul. Moreover, South Korea is currently leaderless, as it plods through the aftermath of Yoon Suk Yeol's martial law decision. Seoul's government is thus not positioned to vigorously defend the country's interests over the next few months, a critical period to set the tone with Trump 2.0.

The government under acting President Choi Sang-mok is trying to put a brave face on its provisional efforts to engage the incoming Trump administration, but Choi has admitted that political uncertainty has undermined those efforts. Even in an optimistic scenario, over the next few critical months South Korea will miss opportunities to shape Trump administration policy, and in the short-term, risks being sidelined from Washington's focus. This is simply an artifact of not having a South Korean president and government who can speak with the mandate of the people, mixed with the reality that any political agreements made now by Seoul could be undone by a potentially incoming Democratic Party of Korea (DPK) president. Alternatively, in the worst case, Seoul's leadership vacuum and consequent vulnerability might attract the predations of Trump, who could force the issue of renegotiating the Special Measures Agreement (SMA) or the Korea-U.S. Free Trade Agreement during a period in which South Korea's government would have less leverage.

Indeed the best hope for Seoul might be that Trump's team focuses on de rigueur policy reviews, domestic affairs, the Russia-Ukraine war and other issues peripheral to Korea and East Asia for long enough that South Korea can return to normal political functioning following a special presidential election (or, less likely, the restoration of Yoon to power).

Regardless of the timing, however, South Korea will likely see a number of critical, challenging issues requiring attention to and cooperation and coordination with the U.S. The first and most obvious is Trump's tariff plans, which include 60 percent tariffs on imported goods from China, 25 percent on goods from Mexico and Canada, and 10 percent universally on imports from all other countries. Frankly, if South Korea does not already have government and private sector plans for dealing with this issue, it is probably too late.

A second major issue is the aforementioned SMA under which South Korea provides host-nation support to the U.S. for its military presence on the peninsula. Trump and members of his security and foreign policy team have already indicated they are dissatisfied with the recently renegotiated SMA, and thus, may push for alterations. Given that eventuality, the Choi government — as well as its successor — would enter discussions with two tools at its disposal: the fact that South Korea is currently the top source of foreign direct investment into the U.S., and the importance of South Korea as a partner in balancing China's rise. Those planks are a solid foundation for arriving at a re-renegotiated SMA figure Seoul could find acceptable.

South Korea should be careful, however, in overselling its role as an ally in balancing China. From a South Korean perspective, not only is the alliance still fundamentally about deterring North Korea, but South Korea's economic, diplomatic and security/defense exposure to China is significant enough that it does not want to antagonize Beijing. This could become tricky, however, as several Trump 2.0 senior officials are on the record demanding South Korea's greater implication in cooperating with the U.S. to contain China. This is arguably the area with the greatest potential for a Washington-Seoul clash, especially if the DPK — which is more China-friendly and U.S.-lukewarm than the Yoon administration — captures the presidency following a special presidential election.

Beyond those three issues, there are many other challenges that will test South Korea's alliance management skills: moving forward (or not) trilateral relations with Japan and the U.S.; maintaining integrated, extended nuclear deterrence despite Trump's erratic rhetorical record on the topic; deciding whether to test the possibility of advancing South Korea's nuclear weapon latency and coordinating with the U.S. on policy toward North Korea, which could careen from crisis to diplomacy (and would have a different valence depending on whether the South Korean president is conservative or progressive).

In some respects, all of the above issues in alliance management have already been present in one form or another, but rarely have they been present in such a complex international environment, and never after a failed self-coup attempt by a South Korean president. Not only has the current crisis weakened Seoul and tarnished its international image (which will negatively affect Trump 2.0's perception of South Korea), but the next weeks and months of Constitutional Court hearings and insurrection trials may produce revelations, notably about the potential misuse of the South Korean military during martial law, that could undermine U.S. faith in South Korea's reliability. This would be another headache for Seoul's alliance managers.

Mason Richey is a professor of international politics at Hankuk University of Foreign Studies, president of the Korea International Studies Association and editor-in-chief of the Journal of East Asian Affairs.