The recent trilateral summit between the leaders of South Korea, the United States and Japan on Aug. 18 was heralded as a turning point in trilateral security cooperation. US President Joe Biden hosted South Korea's President Yoon Suk Yeol and Japanese Prime Minister Fumio Kishida for a summit at the Camp David presidential retreat. The leaders agreed to form a quasi-alliance in the face of the growing threat from China. They agreed to cooperate on a range of security-related issues and to hold annual trilateral meetings of Cabinet-level and other senior government officials.

The US has defense treaties with South Korea and Japan and has long urged both nations to develop closer ties. Since the normalization of relations between South Korea and Japan in 1965, the two countries have developed a close relationship centered on trade, tourism and cultural exchanges. However, acrimony over historical interpretations of Japan’s 1910-45 colonial rule of the Korea Peninsula has made it difficult to develop closer security ties. Politicians and mass media in both countries use this bitterness to bolster their nationalist credentials.

In this context, the development of a security cooperation structure between South Korea and Japan was a major step forward. US President Biden has long considered himself a foreign policy wonk, and he can be justifiably proud of his accomplishment. China’s increasing belligerence, more than Biden’s diplomatic skills, is the driving force behind the change.

The elephant in the room, of course, was former US President Donald Trump. Twice impeached and four times indicted, the former president remains in the lead for the Republican nomination. In a race against Biden, a recent average of polls shows him trailing by about 1 percent. A similar average just before the 2016 election showed him 2 percent behind Hillary Clinton, but he went on to win the Electoral College handily. Biden’s 1 percent lead should be interpreted as meaning a Trump victory. For Biden to win comfortably, he would need to expand his lead to the pre-2020 election average of about 5 percent.

So far, the four indictments have helped Trump rally his base and raise money. Pundits, polls and common sense suggest they will weigh on him as he is forced to spend more time in court instead of on the campaign trail. The problem is that Biden’s approval ratings remain low. Among all presidents since Harry Truman, only Jimmy Carter and Donald Trump had lower approval ratings after 952 days in office. Both lost reelection. As long as Biden’s approval ratings remain low, he risks losing to Trump or whomever the Republicans nominate.

What about a non-Trump candidate? Conventional wisdom suggests that such a candidate would support US alliances, as candidates of both parties have traditionally done. The first Republican debate of this election cycle on Aug. 23 suggests otherwise. The traditional, older Republican candidates all remain strong supporters of Ukraine, but younger candidates, particularly 38-year-old Vivek Ramaswamy, are skeptical. Florida Gov. Ron DeSantis is more supportive, but less so than the old guard.

This suggests a generational shift toward a more isolationist stance on alliances. Such generational shifts tend to run deep and cross political lines. Younger voters are less optimistic about the future of the US and want the country to focus on its domestic problems, an attitude that supports isolationism.

So what does all this mean for South Korea? First, it means that Joe Biden is the last of a long line of post-World War II presidents who supported active US involvement in world affairs. He may or may not win reelection, but his successor, whoever that may be, will be more isolationist as younger generations drive that change. The trilateral cooperation that emerged from the recent summit may continue, but more as ceremony than substance.

Second, it means that South Korea must prepare for a wider range of security scenarios. One optimistic scenario would be the rise of a less confrontational leadership in China as the US profile recedes. This would give South Korea some breathing room as tensions in the region ease. A pessimistic scenario, however, would be an increase in Chinese belligerence amid a broader US retreat from the region. This would leave South Korea isolated, except of course for Japan.

Playing out other negative scenarios reveals a close alignment of interests between South Korea and Japan. As a precaution, the two countries should find ways to deepen their relationship beyond what was agreed to at the recent Camp David summit.

By Robert J. Fouser

Robert J. Fouser, a former associate professor of Korean language education at Seoul National University, writes on Korea from Providence, Rhode Island. He can be reached at robertjfouser@gmail.com. -- Ed.