A New Moon Over the US-South Korea Alliance

On May 9, 2017, South Korean voters went to the polls and elected Moon Jae-in of the left-leaning Democrat (Minjoo) Party their new president. The election closed the chapter on a turbulent seven months in South Korean politics that began with the uncovering of a Samsung tablet belonging to Choi Soon-sil, a confidante of former President Park Geun-hye, leading eventually to Park's impeachment and imprisonment. After historic public protests and a remarkable display of "people power," South Koreans successfully stress-tested their democracy and elected a new leader.

Moon received 41 percent of the vote and became the first candidate in the country's history to break the regional east-west divide between liberal and conservative candidates, taking Busan in addition to Seoul and Gwangju. In a poll conducted days after the election, more than 80 percent of South Koreans expressed their confidence that Moon would manage affairs of state deftly. All in all, Moon Jae-in has a strong democratic mandate, but multiple challenges lie ahead for Moon in the realm of foreign affairs.

Four days after Moon's inauguration, North Korea launched a new type of ballistic missile – the longest-range ballistic missile it has tested to date, in fact. Dubbed the Hwasong-12, the missile was tested successfully over North Korea and into the Sea of Japan, and is thought to have a range of 4,500 kilometers when flown to full range. Moon, meanwhile, wasted little time after coming into office before tackling the North Korea issue; after all, Pyongyang carried out nine missile tests in 2017 while South Korea was under the leadership of Hwang Kyo-ahn, Park's prime minister and, ultimately, caretaker president after her impeachment in December 2016. In his first days in office, Moon spoke to Japanese Prime Minister Shinzo Abe, Chinese President Xi Jinping, and Russian President Vladimir Putin.

And then, there was, of course, U.S. President Donald J. Trump. Moon spoke with Trump, the leader of South Korea's most important ally, on his first day in office. His election ended up highlighting a curious coincidence in the management of the South Korea-U.S. alliance over the past  two decades. Broadly speaking, whenever a liberal favoring engagement with North Korea comes to power in South Korea, the United States tends to be led by a Republican favoring punitive sanctions and pressure.

Moon's mentors, Kim Dae-jung and Roh Moo-hyun, shared their time with the Bush administration while Barack Obama worked with Lee Myung-bak and Park Geun-hye. Kim and Roh oversaw the heyday of the “Sunshine Policy,” which saw the establishment of the Kaesong Industrial Complex and multiple inter-Korean summits. Meanwhile, Lee presided over the most serious kinetic escalation between the two Koreas since the end of the Korean War with the 2010 sinking of the Cheonan and the shelling of Yeonpyeong Island. Park closed Kaesong after North Korea's fourth nuclear test and pursued a standoffish policy of confrontation.

Where, then, will the alliance head under Trump and Moon? Not only is Moon widely expected to examine engagement with North Korea – he said he would travel to Pyongyang under the "right conditions" shortly after his election victory – but Trump by no means will make matters easy. Consider that days before the South Korean election, Trump, in an unedited interview, suggested that Seoul pick up the tab for the controversial Terminal High Altitude Area Defense (THAAD) system. Moon had opposed the system in 2016, when the United States and South Korea decided that it would be deployed. Trump additionally expressed his displeasure with KORUS, the U.S.-South Korea free trade agreement.

Alliances tend to be easier to bend than to break. Even as Trump harps on issues like THAAD, KORUS, and South Korea's host nation support payments, the threat from North Korea continues to grow. The Hwasong-12 test was a reminder that Pyongyang continues to march ahead with its ballistic missile and nuclear programs; alliance discord will do little to assuage concerns about a preemptive strike in North Korea.

One of the greatest challenges to the alliance may come from the specter of “decoupling” – a Cold War concept that may soon acquire new salience in Northeast Asia for both Seoul and Tokyo. During the Cold War, London, Paris, and Bonn worried that once the Soviet Union successfully flight-tested its intercontinental-range nuclear delivery systems and held the U.S. homeland at risk, Washington's security assurances would prove incredible. After all, why would the United States risk a nuclear strike on New York or Washington, D.C., to come to the defense of West Germany?

During the presidential transition, Trump implied that a North Korean intercontinental ballistic missile capability may prove a “red line” of sorts for his administration, taking to Twitter to say that it "won't happen." The Hwasong-12 – a single-stage liquid-fuel intermediate-range missile – may be, if not an ICBM subsystem itself, a stepping stone to an ICBM. Should Trump see out his four years in office, he may preside over North Korea's first successful ICBM flight test.

In this context, it is easy to imagine a scenario where Trump, who marched into office surrounded by chants of “America First,” asks why the United States should risk Los Angeles or West Palm Beach, Florida for Seoul, Busan, or Tokyo. Even if matters don't progress quite this far, Moon's intent to reduce tensions with Pyongyang could lead to a degree of frustration in Washington. It's unlikely that Moon will introduce anything close to the original Sunshine Policy given how much the international sanctions regime and even South Korean domestic law has tightened around North Korea, but his temperament is one favoring engagement.

Under Trump and Moon, the U.S.-South Korea alliance is likely to head into uncharted territory, not just because of the vastly different temperaments of the two leaders, but also because of exogenous factors, including North Korea's unprecedented scale of weapons testing. A crisis, however, isn't an assured outcome. Alliances, like all institutions, have barriers to change and run deeper than the leader-to-leader level. Moreover, underneath the surface of Trump's bluster, U.S. policy toward North Korea remains squarely in the same space as the Obama administration's "strategic patience" approach.

Both Trump and Moon will find that the urgency of the North Korean threat will leave little idle time to relitigate matters like THAAD and KORUS. Pyongyang has been carrying out ballistic missile tests at a rate of roughly two every month since February, after conducting 24 tests in 2016. The clock is ticking and both leaders must ensure that the alliance is up to the task of managing an ever-growing threat.