Japan and South Korea were stable U.S. allies. Not anymore.

For decades, U.S. security in Asia has depended on a network of allies, with Japan and South Korea the two most reliable.

Washington has been able to count on their help to maintain peace in the Indo-Pacific and further American interests. But with new leaders in all three nations and domestic political priorities taking precedence, the strength of these ties is in limbo, jeopardizing U.S. supremacy in the region.

Japan, a treaty ally, is a central pillar of U.S. policy in Asia. The relationship shares similarities to the ties the U.K. has with America, akin to an Asian "special relationship.” Tokyo’s strategic position in countering China’s growing regional influence is a modern-day parallel to Britain’s role in countering German dominance in Europe during the last century, notes Mohammed Soliman, nonresident senior fellow in the National Security Program at the Foreign Policy Research Institute. It is also one of the four largest economies in the world and regularly tops foreign investment charts in the U.S., pouring in funds into at least 39 states.

South Korea is another key aspect of the network. Ties with Washington have helped it to deter North Korea’s growing nuclear ambitions. The U.S. military has maintained a large presence in South Korea since the end of the Korean War, and has approximately 28,500 troops based there. Most are stationed at Camp Humphreys — the largest overseas U.S. military base — allowing America to have a presence in a volatile neighborhood and keep a watchful eye on Pyongyang.

But the landscape has changed drastically in the last few months.

Japan’s Liberal Democratic Party lost its parliamentary majority in an election on Oct. 27, creating an air of instability around the government when the region is already in flux. Prime Minister Shigeru Ishiba has already said he wants to work closely with U.S. President Donald Trump and elevate the relationship even further. The worry is the Trump will pull out of even more multilateral frameworks, leaving Tokyo on its own to deal with China’s growing assertiveness. As one Japanese diplomat told me recently, if the U.S. isn’t willing to defend places like Taiwan or its interests in the Indo-Pacific, there is no reason for Tokyo to step in.

That hedging strategy is already becoming evident. Japan is still smarting from Washington rejecting the Nippon Steel deal on national security grounds, a measure the diplomat described as irrational at best, insulting at worst. Tokyo is hoping to host Chinese President Xi Jinping as a way to keep its largest trading partner onside as it tries to navigate what the U.S.-Japan alliance under Trump will look like. Ishiba’s decision to signal he is interested in closer ties with China has raised concerns inside and outside Japan.

South Korea is also weighing up its options. It is in the midst of a complex political crisis that has paralyzed the economy and governance since President Yoon Suk Yeol declared martial law on Dec. 3. He is facing insurrection charges and the ensuing court battle has become a lightning rod for political divisions, sparking at times violent protests.

Under Yoon — along with former leaders Joe Biden and Fumio Kishida — the U.S.-Japan-South Korea alliance strengthened to new levels. But the recent chaos has meant there will be a new president in Seoul within the year and the most likely candidate is the opposition leader, Lee Jae-myung. He’s implied in the past that he won’t be as friendly to Washington as his predecessor.

The biggest wild card, though, is Trump himself. He’s been vocal about wanting Asian partners to increase their defense budgets. In the years since Trump’s first term, Japan has decided to boost its defense capabilities and spending, although military experts agree that it could do more. Any delay won’t endear it to the new U.S. administration, which is already doubling down on its "America First” approach to multilateral frameworks.

Seoul is already getting a taste of that. In a break from policy, Trump this week called North Korea a "nuclear” power, something that Washington has refused to acknowledge despite Kim Jong Un’s growing arsenal. And he’s previously vowed to make South Korea pay billions of dollars more every year to host U.S. troops.

Instead of moving further apart, the three countries need to work even more closely together to ward off the twin threats from Beijing and Pyongyang. A recalibration of policies and priorities will be necessary to ensure that trilateral cooperation is effective and sustainable, as the Australian Strategic Policy Institute notes.

The three nations should prioritize joint investments in critical technologies, such as semiconductor manufacturing and artificial intelligence, to reduce dependency on China. Boosting cooperation in defense systems would further enhance the alliance’s ability to respond to emerging threats. At a time of deep political divisions, a focus on public diplomacy would help bring citizens along.

The reality, however, is that Trump’s transactional approach to even partners and allies will make these goals difficult to achieve. Asia has already been destabilized by a rising China and volatile North Korea. Cooperation, not further conflict, is the way forward.