SEOUL — South Korea’s newly minted president, Lee Jae-myung, should be on the phone with President Trump in the next day or so, when the two are expected to talk about such hypersensitive issues as tariffs and security.

Almost immediately after Mr. Lee formally took office, his representative told Korean reporters that aides were setting up the exact time for the crucial conversation — something that was so elusive in the six-month hiatus between a failed attempt at martial law and Tuesday’s “snap election” for a new president.

As far as Koreans are concerned, the chance for their leader to chat with the American president comes not a moment too soon. Mr. Trump has just imposed 50 percent tariffs on steel and aluminum, on top of 25 percent tariffs on motor vehicle imports and 10 percent on almost everything else.

Mr. Lee “has high-stakes foreign policy challenges” including economic issues, a professor at Tufts University’s Fletcher School, Aram Hur, said.  The question, she said, talking at the Korea Society in New York, is “how to balance the U.S. alliance” with “economic pressure,” from China, Korea’s biggest trading partner and an aggressive investor in Korea’s economy.

Mr. Lee may not be able to persuade Mr. Trump to suspend the tariffs right away, but he is sure to profess his desire to strengthen the Korean-American alliance while rebuilding strong relations with Communist China.

Intrinsic in achieving those conflicting goals is the need to buttress an economy that the Korea Development Institute says is increasing by less than 1 percent this year, in stark contrast to the double-digit rises of previous years. In the “battle against recession,” Mr. Lee said in his inaugural address, he plans to set up an emergency task force “to revive a virtuous economic cycle.”

Mr. Lee’s dealings with Mr. Trump will raise the issue of how to redefine the basis of this alliance, Ms. Hur said. Even if Mr. Trump wants to withdraw some of America’s 28,500 troops from Korea, “U.S. troops based in South Korea are clearly a hedge against China,” she noted. Linkage of economic and security concerns appears inevitable. 

For Mr. Lee, that he’ll be talking to Mr. Trump at all represents a sharp improvement over the past six months, when significant communications between leaders in Seoul and Washington were virtually nonexistent.

The man who was serving as “acting president,” Han Duck-soo, a former ambassador to Washington, did get through to Mr. Trump in April, but the conversation was pro forma — Mr. Han did not have the authority to make deals in the vacuum created by the impeachment of the conservative Yoon Suk-yeol as president in the aftermath of his ill-fated attempt at imposing martial law on December 3. Mr. Trump had turned down previous entreaties to talk.

Mr. Lee is widely expected to pull back from the close ties formed with Washington during the Biden presidency. To the delight of President Biden, Mr. Yoon endorsed large-scale joint American-Korean military exercises that the previous Korean president, the leftist Moon Jae-in, had banned. American military officials are waiting anxiously to see if Mr. Lee approves annual American-Korean war games set for August.

Mr. Lee may be more interested in reviving talks with North Korea’s leader, Kim Jong-un, who has refused to deal with South Korea since Mr. Trump stalked out of their summit in Hanoi in February 2019. “We will keep channels of communication with North Korea open and pursue peace on the Korean Peninsula through dialogue and cooperation,”  he said at his inauguration. 

Mr. Kim, however, now has formed close ties with President Putin, to whom he agreed to provide arms, ammunition, and even troops for his war against Ukraine.

Yet what if Mr. Lee convinces Mr. Trump of his influence with Mr. Kim? If he “can bring North Korea back in a way that helps Trump’s ambition to be a global peace-maker,” Ms. Hur said, “that can become a bargaining chip in a three-way triangulation.”

Mr. Lee’s desire to see Mr. Kim may make it difficult, though, to uphold the trilateral deal formed by Mr. Biden, Mr. Yoon, and Japan’s then-prime minister, Fumio Kishida, at Camp David in August 2023. “You can’t have both North Korea and Japan,” Ms. Hur said. “If South Korea had to choose, it would try to bring North Korea back into the fold. I’m skeptical how relations with Japan will be pursued.”