SEOUL — “The Spirit of Camp David” is at stake in a controversial decision that President Biden could make soon on the sale of one of the greatest names in American industrial history, U.S. Steel, to Japan’s largest steel maker, Nippon Steel.

To appearances, the $15 billion deal has nothing to do with the pledges made at Camp David more than a year ago by Mr. Biden, Prime Minister Kishida of Japan, and President Yoon of South Korea for mutual defense against North Korea and its regional allies, China and Russia.

The looming steel deal, however, has everything to do with American security, raising the hypersensitive question: how much can Washington trust Tokyo nearly eight decades after the end of Japanese rule over the Korean peninsula, much of China and Southeast Asia?.

Distrust between Washington and Tokyo pervades debate on what happens if U.S. Steel falls into Japanese hands as it teeters toward insolvency. In the aftermath of Camp David, the sale of U.S. Steel is almost a test case of the depth of friendship..

The danger of the deal compromising the American-Japan alliance contrasts with the show of friendship displayed by Messrs. Kishida and Yoon at their farewell summit at Seoul — their final meeting before Mr. Kishida steps down this month.

Casting aside numerous differences over unsolved issues like “comfort women” and slave labor during World War II, Mr. Yoon said they at least resolved “to maintain the positive momentum” they had built in 12 meetings, including Camp David, and adopt a “forward-looking attitude” despite the legacy of history.

Simultaneously, in an exercise in formal understatement betraying Japanese concerns about the potential impact of failure of the steel deal, the powerful Japan Business Federation, Keidanren, said simply that it hoped “the review procedure will be conducted with the utmost integrity and fairness in accordance with the law,” according to Japan’s Jiji Press. The deal should be “conducted objectively based on fair rules and processes.”

Jiji quoted the influential Japan-U.S. Business Council as decrying “attempts to politicize the review process.”

The brouhaha has erupted as a political issue that Mr. Biden might prefer to avoid so close to the election, but he is reported likely to block the deal in line with the recommendation of the Committee on Foreign Investment in the United States, headed by the treasury secretary, Janet Yellen.

The presidential candidates, Vice President Harris and President Trump, despite their differences on almost everything else, also oppose the deal, which the United Steel Workers and Pennsylvania’s two senators, Bob Casey and John Fetterman, both Democrats, agree would cost jobs and compromise national security.

The chief executive of U.S. Steel, David Burritt, has warned, however, that U.S. Steel would still have to close plants and does not have funds for the massive upgrading promised by Nippon Steel.

“Skeptics of the threat posed by the deal,” said an analysis by the Council on Foreign Relations, “argue that the acquisition of a U.S. firm by a close ally does not raise obvious security risks.” The lawmakers “leading the anti-deal charge,” said the report,  “benefit from union support and face tough reelection contests.”