When Antony Blinken became the No. 2 at the State Department during the Obama administration in 2015, his mandate was clear: Focus on Asia.

The rocky relationship between two crucial Asian allies, Japan and South Korea, had deteriorated over the issue of wartime sex slaves. Later that year, with the help of the United States, the two countries reached a landmark agreement to resolve their historical dispute.

Blinken had initiated a series of three-way talks, marking the first time the American deputy secretary of state had met with his counterparts in Japan and South Korea. He insisted they meet every three months to build a habit of working together, signaling that the relationship was a priority to the United States, experts say.

Now as President Biden’s secretary of state, Blinken is tasked with re-energizing American alliances that were strained under the Trump administration’s “America First” approach.

Relations between Japan and South Korea are once again at one of their lowest points in decades. Whether the United States can nudge the two countries into cooperation will be highly consequential for the Biden administration’s ambitions to restore trust abroad and effectively counter China’s rise and North Korea’s nuclear capabilities with a coalition of like-minded allies, experts say.

“When there’s a serious rift in the family, it’s hard to invite your friends over for dinner,” said Daniel Russel, an Asia Society expert who was a high-ranking foreign policy official in the Obama administration.

“Given the magnitude of the challenges that we face from North Korea, China, et cetera . . . we can’t afford to be operating at anything less than full speed,” Russel said. “There’s a broken circuit in our network at a critical junction, and it is imperative that that somehow get fixed.”

The State Department last month held its first meeting with top diplomats in Japan and South Korea to discuss North Korea-related challenges. A senior State Department official said the meeting was intended to send a strong signal that the administration, in its first full month in office, is committed to restoring its relationship with the two countries.

The Biden administration is still reviewing next steps on improving the three countries’ relations, but “you can absolutely count on seeing a greater effort put into reinvigorating trilateral cooperation, along with strengthening our respective alliances with Seoul and Tokyo,” said the official, speaking on the condition of anonymity to describe diplomatic matters.

The administration may soon have an opportunity to help jump-start cooperation between its two allies, with South Korean President Moon Jae-in saying Monday that his government was open to talks with Japan.

While Blinken, a veteran diplomat, is in many ways uniquely fit for the moment, he must contend with the shifts in U.S. allies’ political and strategic calculations under Trump.

Despite the progress made in 2015, the relationship between Japan and South Korea has deteriorated in recent years over legal and economic disputes, with little political incentive for either country to mend ties.

Trump noticeably took a passive role in maintaining a relationship with both nations, instead becoming singularly focused on whether they were paying enough money to keep U.S. troops stationed in their countries. He questioned long-standing treaties and international agreements, and undermined allies’ confidence that the United States would defend them.

Some allies are concerned that the whiplash return to alliances under Biden could be temporary, given that the U.S. election was not a resounding rebuke of the Trump era, experts say.

“You can’t just say, ‘Trump is gone, it’s a return to status quo prior to Trump.’ There’s going to be a lot of allies thinking, ‘Okay, someone like Trump can return again,’ ” said Frank Aum, senior expert on North Korea at the U.S. Institute of Peace and a former senior Pentagon adviser. “That being said, I think a lot of our South Korean and Japanese allies are probably very excited to see the Biden administration because of how strong and invested the Obama administration was.”

While allies in Asia generally welcome America’s return to a traditional approach to diplomacy, they must now weigh new considerations about their place in the U.S.-China competition, which has only intensified in the past four years, said Yoshihide Soeya, a professor emeritus at Keio University in Tokyo who has studied the trilateral relationship.

“Asian allies of the U.S. have to think in a really serious [way] strategically about the place and the role of the U.S. at this time of mega-competition between China and the United States, and it’s not an easy situation,” Soeya said.

He added that in many ways, it was simpler for allies to navigate Trump’s approach.

“The Trump period, it was only about money,” he said. Now, the United States is “essentially saying, ‘You should talk and you should cooperate, not necessarily for the sake of Japan and South Korea but for the sake of American regional re-engagement.’ So the responsibility on our part, in this case, Japan and South Korea, is also much greater under the Biden administration.”

Still, many point to the fact that Blinken is a known and trusted figure in Asia and elsewhere as an advantage for the Biden administration.

“The last four years, they were contending with a United States that was speaking in a language they didn’t understand,” said Victor Cha, the Korea chair at the Center for Strategic and International Studies and former top adviser on North Korea in the George W. Bush administration. “The United States has to signal stability, reliability, predictability and a willingness to lead, but also have allies play a large part. And Blinken personifies that.”

As deputy secretary of state, Blinken stressed that he wanted to meet quarterly with his counterparts in Tokyo and Seoul, and made sure that his staff followed up on specific items after the meetings, according to those who worked with him.

South Korean officials were stunned that Blinken wanted not only to consult with his counterparts for the first time but also to meet regularly at his level, said a South Korean official who worked on trilateral issues, speaking on the condition of anonymity to describe private discussions. They had assumed he would want to meet twice a year at most, given the breadth of issues under his purview.

Notably, Blinken encouraged the three countries to think creatively about how to cooperate, beyond their long-standing shared concerns over the North Korean nuclear threat. In a March 2016 speech at the Brookings Institution, he outlined the American vision for new issues that the allies could work on together, including climate, gender equality, humanitarian assistance, counter-piracy issues, cancer research and space exploration.

“This is something that then-deputy secretary Blinken really, I think, helped to lead and was the inspiration behind,” the senior State Department official said.

Broadening the scope of the discussions beyond North Korea signaled to the South Koreans and the Japanese that Blinken was serious about working closely with them, said the South Korean official.

“Tony is now secretary of state, so he has such a huge responsibility covering all areas. I don’t know if he will be personally involved,” the official said. “But if the trilateral cooperation renews . . . I would believe that Tony Blinken is behind that, with his fingerprints all over it.”