KEI Spotlight

This article was published in The Diplomat on March 30, 2024.

Nowadays conversations with South Korean counterparts begin and end with concerns about former U.S. President Donald Trump’s possible return to the White House. Questions abound regarding tariffs and trade, industrial policies and export controls, unilateral attempts at accommodation with North Korea, and the issue of cost-sharing and U.S. forces in South Korea. This array of issues demonstrates an incredibly multifaceted South Korea-U.S. alliance. Yet, if so many aspects of the relationship simultaneously could be open to question under a second Trump administration, it raises broader concerns about the alliance’s longevity.

Among them, no other issue cuts to the core of the alliance more than the question of U.S. forces on the Korean Peninsula. For all the pronouncements about the broadening and deepening of the alliance beyond its traditional military and defense components – into a strategic economic and technology partnership and global comprehensive strategic alliance – the U.S. force presence is the keystone in the arch upon which all else was built. Shift the stone and the arch teeters.

Trump’s past behavior and statements presage such shifts in the future.

Historical Context

Since the 1960s, Democratic and Republican presidents alike have pushed for greater cost-sharing (and burden-sharing) from Seoul and reassessed U.S. forces in South Korea. And the two issues were, to a degree, interconnected. Seoul’s remarkable economic growth not only provided the wherewithal to contribute more to the stationing of U.S. forces but also modernize the Republic of Korea (ROK) military. The latter resulted in South Korea gradually taking over various missions from U.S. forces and establishment of a combined alliance structure, within which U.S. and ROK forces divided labor in a more balanced manner. These developments, alongside shifting strategic contexts and U.S. foreign policy priorities, drove U.S. policymakers to gradually reduce and realign the U.S. presence.

The early post-Cold War period is a key example. Propelled by calls for a peace dividend at home and for allies to do more abroad, coupled with reduced tensions globally and around the Korean Peninsula, the George H.W. Bush administration structured a 10-year, three-phase plan for force reductions and realignments in South Korea and the wider region known as the East Asian Strategic Initiative (EASI). As part of the policy, South Korea would eventually take the lead role in its own defense and the alliance’s command structure.

In this context, the Special Measures Agreement (SMA) framework was first established and codified. Under the SMA, South Korea provided financial support for a percentage of the total non-personnel costs of the U.S. military presence in South Korea, broken down into three categories: labor costs (i.e. salaries for the Koreans who work on U.S. bases); logistics and supply costs; and military construction costs. Although EASI was paused after its first phase – due to the first North Korean nuclear crisis and U.S. need to maintain primacy in the region – Seoul gradually continued increasing contributions under successive SMAs.

However, U.S. policymakers did not adjust the U.S. force presence based upon Seoul’s level of contribution. For them, it went without question the presence was critical to maintaining stability and deterrence on the peninsula and bolstering strategic imperatives beyond it. Trump rejected such assumptions.

Enter Trump

During the 2016 campaign, Trump lambasted all U.S. allies for free riding. Unfortunately for South Korea, its cost-sharing deal was the first to come up for renegotiation. Trump directly liked the issue of cost-sharing with the U.S. presence. He saw U.S. forces as there solely to defend South Korea and rejected (or seemed not to understand) their broader strategic logic. The United States got “practically nothing compared to the cost,” Trump said.

Never mind that by the time Trump entered office in 2017, Seoul was covering over $800 million, nearly 50 percent of the non-personnel costs, and had handled roughly 90 percent of the nearly $11 billion in construction costs for Camp Humphreys, the United States’ largest overseas military base. When the SMA renegotiation began in 2018, Trump demanded Seoul double its contribution to cover 100 percent of the non-personnel costs. Seoul refused, and a one-year stopgap deal was signed whereby South Korea boosted its contribution by 8.2 percent to about $920 million, covering roughly half the non-personnel costs.

Soon thereafter, Trump upped the ante, demanding South Korea increase its contribution by 400 percent or $5 billion, which would have meant South Korea would cover the entire $3 billion in direct basing costs while also paying a 66 percent premium. The Moon administration refused Trump’s demand, and, amid a global pandemic, talks stalemated. Korean laborers on U.S. bases were furloughed as budget funds ran out.

Until he left office, Trump refused to accept the Moon administration’s offer to boost its contribution by upwards of 13 percent, instead demanding Seoul pony up $5 billion (with some reports indicating a reduced ask of $4 billion, albeit a still outlandish number). Intent on stabilizing alliance relations, one of the first steps the Biden administration took was to finalize a new SMA, accepting South Korea’s offer to increase its contribution by 13.9 percent.

Notwithstanding the effort by the Biden and Yoon administrations to negotiate a new cost-sharing deal before the 2024 election (despite it not being due for renegotiation until 2025), there is reason to believe Trump would challenge it if elected. The issue could once again metastasize, accelerating Trump’s longstanding skepticism about U.S. troops in South Korea, and resulting in potentially precipitous changes in the U.S. force posture. Such dynamics arose in his first term and, according to various sources and Trump’s statements, would have worsened in a second term.

Presaging the Future?

In a February 21, 2023, post on Truth Social, Trump noted that he got to know and got along well with North Korean leader Kim Jong Un and that Kim was not happy with and felt threatened by South Korea-U.S. military exercises. Such exercises are “extremely expensive and provocative drills,” and South Korea “pays us very little” for them, he claimed. Inaccurately stating that 35,000 U.S. troops were stationed in South Korea, Trump finished: “I had a deal for full payment to us, $Billions, and Biden gave it away. Such a shame!!!”

Would this sentiment be assuaged by another deal under Biden? Additional sources indicate not.

Describing a 2021 interview with Trump in their book, “The Divider,” Peter Baker and Susan Glass wrote: “The only regrets Trump expressed to us were that he was not able to push through all the tough policies he hoped to against America’s allies, whether imposing tariffs on German cars or sticking up South Korea for $5 billion in payment for American troops stationed there – both preoccupations of his he told us he planned to pursue in a second term.”

Covering similar ground recently, Baker reiterated that in addition to trying to reduce troops in Germany (a move rescinded by Biden), Trump “contemplated pulling American troops out of South Korea as well, only to be talked out of it, but has said since leaving office that such a move would be a priority in a second term unless South Korea paid more in compensation.” Other accounts point to more worrisome inclinations.

According to Secretary of Defense Mark Esper’s book, “A Sacred Oath: Memoirs of a Secretary of State During Extraordinary Times,” Trump proposed the “complete withdrawal of U.S. forces from South Korea.” Also, based on conversations with Esper for their book, “I Alone Can Fix It: Donald J. Trump’s Catastrophic Final Year,” Carol Leonnig and Philip Rucker wrote that:

Trump had privately indicated he would seek to withdraw from NATO and to blow up the U.S. alliance with South Korea, should he win reelection. When those alliances had come up in meetings with Esper and other top aides, some advisers warned Trump that shredding them before the election would be politically dangerous. “Yeah, the second term,” Trump had said. ‘We’ll do it in the second term.”

To be sure, it is unclear whether Trump’s proposals to remove all troops or blow up the alliance reflected genuine intent or were merely a function of his hardline bargaining.

Alternatively, Trump may have adopted such an outsized position knowing it would be rebuffed, thus justifying removing some or all the troops. National Security Advisor John Bolton’s account indicates mixed motivations. Amid SMA negotiations in 2019, Trump said a way to get $5 billion was to threaten to withdraw all U.S. forces. “That puts you in a very strong bargaining position,” Trump said. This occurred in a context of increasing North Korean short-range missile tests, which were restarted following the failure of the Hanoi Summit. Trump observed to Bolton, “This is a good time to be asking for the money,” using growing tensions as leverage.

Later, Trump impetuously expressed frustration with ongoing if scaled down alliance military exercises, saying: “Get out of there if we don’t get the five-billion-dollar deal [for South Korean support of US bases]. We lose $38 billion in trade in Korea. Let’s get out.” Whether or not pure bombast, the message had begun to make its way through the inter-agency process.

According to a high-level former defense official, early in the administration the Pentagon fielded questions from the White House about why U.S. forces in South Korea were necessary. Such questions were normal insofar as new administrations conduct policy reviews, including force posture reassessments. However, despite the Pentagon providing detailed feedback, similar questions persisted. That was out of the ordinary. Although many suspected such discussions were occurring given Trump’s open distaste for alliances and foreign commitments, it was not until that 2020 reports emerged indicating the Pentagon had presented the White House with options for reducing U.S. forces in Korea.

One the one hand, the effort could have been a way for establishment types to mollify Trump by presenting him with concrete options. On the other hand, leaking to the press such options were being prepared may have fit Trump’s bargaining strategy. Nonetheless, administration officials declined to offer details about the specific options for reducing forces below the oft-cited 28,500 troop level, saying no decision had been made to reduce them. In any event, at that stage, the pandemic and reelection campaign took center stage, the SMA talks remained stalemated, and Trump went on to lose the 2020 election.

Trump’s views on the issue likely have not changed. The above (and other) sources provide insight into how Trump might approach the SMA and the broader question of U.S. forces in South Korea were he to be elected in November, including potential demands he might make, what he might do if those demands are not met, and various challenges and opportunities this may present.

Trump’s Possible Demands and Questions Raised

It appears plausible that even if the Biden and Yoon administrations sign a new agreement before the November election, Trump will not accept it. He may even target it during the campaign. Moreover, if elected, Trump likely intends to shake up the Department of Defense (DoD) and other executive branch departments and agencies far more than in his first term. His approach would potentially combine pushing out large numbers of civil servants by demoralizing or defunding them while targeting specific appointees and placing loyalists in their place, hammering the inter-agency into a more plaint operation. Foreign policy establishment types may either be barred at the door or be specifically selected to carry out his preferences.

Additionally, based on current trends, Trump would enter office at a time when North Korea is advancing its nuclear and missile capabilities in unabated fashion, inter-Korean tensions are at a high, and the alliance has ramped up and regularized military exercises alongside U.S. strategic asset deployments and efforts to institutionalize the Nuclear Consultative Group (NCG). In this context. Trump not only could demand Seoul cover 100 percent of non-personnel costs in the three categories under the SMA framework but also the costs of strategic asset deployments or other rotational units that make up important parts of the U.S. force structure. In other words, he would demand cost-sharing expanded beyond the existing SMA framework, consistent with demands during his first term.

Trump may see a worsening North Korea threat – and well-known South Korean insecurities – as the leverage he needs, again consistent with his comments during his first term. Although the conservative Yoon administration is more inclined to lean toward the U.S. position than its progressive predecessor, it could hardly accept these demands. Trump may then be predisposed to downgrade or call off continued exercises and strategic deployments, thus accelerating extant conversations regarding U.S. credibility and an indigenous South Korean nuclear capability (an idea he supported in 2016).

Alternatively, if Seoul does offer to cover some of the U.S. strategic asset or rotational deployments, does that mean the Trump administration would provide its Korean counterparts greater visibility and say about how and when such deployments operate? Such demands already increased under Biden, despite the Washington Declaration and gradual implantation of the NCG. It seems most likely, however, that Trump would push Seoul to give more, while expecting it to see and say less regarding U.S. operations. If America First logic predominates in cost-sharing discussion, will it disappear when it comes to highly sensitive areas like U.S. nuclear policy and planning?

Furthermore, since Trump is inclined to make demands that no ally would be willing or able to meet – given their own substantial domestic political barriers – he will potentially do what he was unable to do in his first term, namely, remove at least some U.S. forces. During Trump’s first term, Congress passed bipartisan language in successive National Defense Authorization Acts (NDAAs) precluding the Pentagon from reducing troops in South Korea (below 22,000 in the 2019 NDAA and and 28,500 in the 2020 NDAA) without the defense secretary certifying the North Korean threat had eased, and the reduction would not hurt U.S. national security. Congress removed such language under Biden.

Yet, even if Congress reintroduces such legislative language under Trump, what’s to stop a unilateral push to improve relations with Kim Jong Un and a plaint secretary of defense from certifying such conditions? Besides, Trump would be the commander-in-chief, able to dispose of U.S. forces how he chose. Congressional opposition would complicate the process but not necessarily stop it.

Searching for Clues 

Christopher C. Miller, the former acting secretary of defense at the tail end of the Trump administration, wrote the section on defense issues in the Heritage Foundation’s “Mandate for Leadership,” a comprehensive policy guide for the next conservative U.S. president many have examined for potential insights into a second Trump administration. In it, he called for U.S. allies to take far greater responsibility for their conventional defense and for Washington to “Enable South Korea to take the lead in its conventional defense against North Korea.” More recently, Miller said in an interview it was time to discuss whether South Korea still needs 28,500 American troops or if change was needed.

One potential step Trump might take would be to cancel the next deployment of the 4,400-person Stryker Combat Brigade Team (SCBT), which deploy to South Korea on a nine-month rotational basis from different U.S.-based locations. In other words, once the existing SCBT deployment leaves, Trump might bar the next from going. In 2020, congressional staffers expressed this exact concern. Notwithstanding the fact that South Korea already handles the overwhelming conventional burden on the Korean Peninsula, removing the SCBT would surely force the issue.

The SCBT – transformed from a U.S. Army Armored Brigade Combat Team (ACBT) in the fall of 2022 – provides additional firepower capability and mobility. It is the last remaining U.S. ground-maneuver, infantry formation in South Korea and a critical element of the 2nd Infantry Division/ROK-US Combined Division, itself the last remaining permanently forward-stationed division in the U.S. Army.

Were the SCBT removed from South Korea, the U.S. footprint would still be well over 20,000 troops, made up of (among other units) an aviation brigade and field artillery brigade, considerable air force, space, and intelligence capabilities, and a division headquarters capable of handling the logistics of folding in additional off-peninsula forces deployed to South Korea in the event of a contingency. Still, such a reduction would compel Seoul to take on an even greater burden while it increasingly grappled with its own military manpower shortages given its demographic decline.

Additionally, might a second Trump administration try to push Seoul to accept the more regular and flexible use of U.S. forces in South Korea, including elements of the SCBT or 7th Air Force, to deal with broader regional operations? This would also be consistent with the “Mandate for Leadership’s” recommendation for U.S. allies to play their part in dealing with China as well as statements from defense officials late in Trump’s first term that future force posture decisions would be less about bases and more about places. Furthermore, it would build on the fact that elements of the 7th Air Force already participate in wider regional exercises, including this month’s Cobra Gold exercises in Thailand (which also included personnel from South Korea, Indonesia, Japan, Singapore, and Malaysia) and aerial refueling operations over Okinawa in January.

Maybe the tradeoff would be a lower cost-sharing demand in exchange for acceptance of a more networked alliance system wherein U.S. forces moved more flexibly and freely to, through, and from the Korean Peninsula. This is what U.S. policymakers conceptualized in the early-to-mid-2000s during debates about strategic flexibility. South Korean officials have pushed back against the idea then and since.

Reflexive Opposition Won’t Suffice

For many South Koreans in defense and national security circles, when it comes to the SCBT, its symbolic importance exceeds its potential warfighting role. Despite the notable evolution and reduction of the so-called U.S. tripwire in South Korea, elements of the SCBT remain north of Seoul (others are south at Camp Humphreys). Indeed, South Korea’s entire national existence has been defined by some form of U.S. ground combat presence north of the capital city. The only time when this was not the case was from June 1949 to the outbreak of the Korean War a year later.

That history is deeply embedded in the Korean national security psychology. It helps explain the profound opposition to President Jimmy Carter’s policy to remove all remaining ground combat troops in the late 1970s and partly why he failed to implement it. The history persists in the present.

When I broached the possibility of removing the last ground-maneuver, infantry formation with former South Korean officials in early 2020 – moving toward a more flexible air- and naval-centric U.S. posture – they categorically rejected the idea. It was not so much about the mechanics of warfighting as the shadow of history. The SCBT’s withdrawal – or it and other units’ flexible use for off-peninsula contingencies – would reawaken a longstanding, if contradictory mix of abandonment and entrapment fears. More recently, in response to Miller’s comment, South Korean Defense Minister Shin Won-sik insisted the current size of U.S. troops stationed in the country was “absolutely necessary.”

Still, just because changes in the U.S. force structure may cause tremors in South Korea or opposition in Congress is not sufficient reason to avoid contemplating them. The 28,500 number was a floor, set in 2008 and reflexively repeated since. Truculently adhering to that number is neither sound policy nor does it allow for constructive, forward-thinking planning; not to mention the fact that the number is never actually at 28,500 but fluctuates above and below it at any given time. The uncertainty of just how exactly Trump will approach U.S. forces in South Korea if reelected, coupled with his well-recorded skepticism, is both cause for concern and reason to constructively explore alternative futures.

As I’ve explored elsewhere, there may be creative ways to reduce the U.S. footprint, enhance alliance integration, and enable Seoul to take on greater responsibility and authority while simultaneously taking on greater defense burdens in the alliance. It is better to ask hard questions and explore creative solutions now rather than wait for potentially impetuous demands from Trump. Doing such work ahead of time will help in the event that he is elected.

As my colleague Mark Tokola rightly notes, Trump’s demands should be read as opening bids, not final positions, and his policy pronouncements as first drafts rather than final products. Trump’s lack of convention, though certainly concerning, opens space for Seoul’s own creativity in making counter-demands. That requires it move away from knee-jerk opposition to change. Instead, it should lead the charge.