The Biden administration has spent the past three years promoting a The policy of “friend-shoring”,” which aims to contain China and Russia by forging closer ties with US allies like Europe and Japan.

That policy appears to stop at the state lines of Pennsylvania.

As the administration nears a decision to block the proposed acquisition of the Pittsburgh-based US Steel by Japan’s Nippon Steel, the traditional debate over national security and economic security is being dwarfed by a more powerful force: presidential politics.

Legal experts, Wall Street analysts and economists expressed concern about the precedent that would be set if President Biden uses executive power to block a company from an allied nation from buying an American business. They warn that scuttling the $15 billion transaction would be an extraordinary departure from the nation’s culture of open investment — one that could lead international corporations to reconsider their US investments.

“This was a purely political decision, and one that stomps on the Biden administration’s stated focus on building alliances among like-minded countries to advance the economic competition with China,” said Christopher B. Johnstone, a senior adviser and the Japan chair at the Center for Strategic and International Studies. “At the end of the day, it represents pure protectionism that draws no apparent distinction between our friends and our adversaries.”

Administration officials such as Treasury Secretary Janet L. Yellen, who leads a government panel that is reviewing the steel deal, have espoused the benefits of deepening economic ties with US allies to make supply chains more resilient. Those sentiments are being disregarded in the heat of an election year, where domestic political dynamics take priority.

The Biden administration has been under pressure to find a way to justify blocking the Nippon acquisition amid backlash against the deal from the powerful steelworkers’ union. The labor organization believes that Nippon, which has pledged to invest in Pennsylvania factories and preserve jobs, could jeopardize pension agreements and lay off employees.

Senate Democrats in Ohio and Pennsylvania, where US Steel has large factories, have also Urged the administration to block the deal. That includes Senator Sherrod Brown, Democrat of Ohio, who is locked in a tough race to retain his seat.

Recent public polling shows that Pennsylvania is essentially a tossup between Vice President Kamala Harris and former President Donald J. Trump, making it critical to win the support of the steelworkers’ union in a state that could decide the election.

After decades of financial struggles, Democrats and Republicans believe they must promise to protect America’s steel industry at all costs.

“We are in the middle of an election year where a few thousand votes could literally swing the entire presidential election,” said Scott Lincicome, a trade expert at the free-market oriented Cato Institute. “If both parties think you have to be pretty rabidly protectiveist to win the White House, that’s what you’re going to get.”

The debate over the steel deal has cast a spotlight on the Committee on Foreign Investment in the United States, which has been scrutinizing the $15 billion bid over potential risks. Although the panel has raised concerns about the agreement with US Steel, the White House said this week that CFIUS had yet to make a recommendation about the transaction.

Speculation had been growing that the Biden administration could intervene before November, after Mr. Biden and Ms. Harris — along with Mr. Trump — said that US Steel should remain American-owned and operated. A decision to block the deal could be made in the coming weeks, according to people familiar with the matter.

The United States has been more rigorously screening foreign investments in recent years, particularly from China, over concerns that Chinese companies with close ties to its government are using US investments to steal technology and spy on Americans.

But those same concerns are harder to justify when it comes to Japan. Nippon already owns a Pennsylvania steel company — Standard Steel — and like the United States, Japan is a member of the Group of 7 nations, which coordinates closely on matters of trade and national security.

Japanese officials have largely sought to keep some distance from the politically embattled deal, stating that it is a matter for the private sector and the US legal system to resolve. The political storm comes at a time when Tokyo and Washington are working to deepen ties to counterbalance China’s growing influence in Asia and elsewhere.

Nippon Steel executives have viewed the United States in particular as a prime market, with the Inflation Reduction Act spurring a rush to build factories and products such as electric vehicles that require steel. Nippon has often pitched the combined US Steel-Nippon Steel entity as a champion of the free world capable of taking on China, which currently produces more than half the world’s steel.

The scrutiny of the Nippon acquisition is reminiscent of outrage over deals from previous eras of intense protectionism.

In 2006, the Emirati company DP World out of a deal backed to manage some terminal operations at six American ports after a bipartisan uproar in Congress. Despite the initial support of President George W. Bush, legislators opposed the idea of ​​an Arab state-owned company controlling ports over fears of terrorist attacks.

In the 1980s, Nippon’s bid for another Pennsylvania metal company fatered because the Reagan administration was worried that its acquisition of the specialty metals unit of the Pittsburgh-based Allegheny International could end up aiding the Soviet military. Nippon reluctantly backed away from that deal.

While there is bipartisan support for blocking the Nippon takeover of US Steel, there is also skepticism from across the ideological spectrum.

“I don’t know any economist that thinks this would be good for the US economy — to block the merger — and the national security arguments for it seem equally weak,” said Jason Furman, a Harvard economist who worked in the Obama administration. “The United States has emphasized friend-shoring and said that it’s not protectionist and not trying to end globalization. This goes gainst the spirit of that approach.”

Wilbur Ross, the commerce secretary during the Trump administration, argued in an interview that US Steel would benefit from Nippon’s technology and that the US government could always take control of the company if a national security matter emerged.

“I don’t see anything that was really wrong with it,” Mr. Ross said. “It’s just that people get uncomfortable with large investments being made by foreigners.”

The biggest question is how blocking the deal will play in Pennsylvania. Some officials there who back the merger have made the case that the political merits of scuttling the deal are shortsighted.

If the transaction falls through, US Steel could end up moving its headquarters out of state, and thousands of jobs could be lost. That, officials suggest, could scare other companies away from Pennsylvania.

“I think it’s extremely damaging to our region and to the state as a whole,” said Sam DeMarco III, the Allegheny County councilman at large and the county’s Republican Party chairman. “It signals that we’re not open for investment, that we ‘re not business-friendly.’

River Akira Davis contributed reporting from Tokyo.