United States Steel Corp. plunged for a second day after President Joe Biden said the company should retain American ownership, coming out against a takeover by Japan’s Nippon Steel Corp. despite the risk of upsetting a key ally.

The stock dropped as much as 11%, and has lost about a fifth of its value in the past two days, when news first broke that Biden would express concern about the deal. The shares are now trading at levels last seen before the Nippon deal was announced in December, suggesting investors are increasingly skeptical about its chances of success amid an ongoing federal review.

“US Steel has been an iconic American steel company for more than a century, and it is vital for it to remain an American steel company that is domestically owned and operated,” Biden said in a statement. “It is important that we maintain strong American steel companies powered by American steelworkers. I told our steel workers I have their backs, and I meant it.”

Biden’s statement marks a rare presidential intervention in a transaction that outside an election year would have drawn less public scrutiny. Despite its storied history, US Steel’s role in the economy has diminished over several decades, a period during which producers in Asia have risen to dominate the global steel market. And while Nippon Steel’s proposed $14.1 billion acquisition targets an iconic business name, a takeover in the US commodities industry by a company based in a friendly country is hardly unusual.

Biden was silent on the pending review of the deal by the Committee on Foreign Investment in the United States, or Cfius, and stopped short of an outright pledge to block it. Cfius is led by the Treasury Department and has the power to approve, block or amend the deal on national security grounds, or send it to Biden for a decision.

“Our transaction delivers clear benefits to US Steel, union workers, the broader American steel industry, and American national security,” Nippon Steel said in a statement on Thursday evening. “No other US steel company on its own can meet this challenge while also meeting antitrust requirements.” 

Timna Tanners, an analyst at Wolfe Research LLC, said the deal suffered from the “unfortunate timing” of being brokered in the midst of an election in which both candidates have vowed to bolster domestic manufacturing and use their power to stop jobs from going overseas.

“The deal is facing a much more difficult chance of going through now that Biden has come out against it,” she said. “It’s an alarming precedent that the US government is setting.”

US Steel fell about 6% in New York on Thursday, dropping more than 30% below the $55 a share being offered by Nippon Steel. US Steel did not immediately respond to requests for comment.

Even though its share of the market has shrunk, US Steel carries heavy symbolic value. It is based in Pennsylvania, Biden’s birth state and a battleground in the presidential election, and embodied the nation’s economic might in the 20th century. 

Read: No Labor Agreement, No Deal: Steel Union Draws Line for Nippon

The announcement of Japanese company’s acquisition triggered opposition from Republican and Democratic lawmakers as well as the influential United Steelworkers union. Biden’s allies have urged the administration to kill the deal over national security concerns and the threat to unionized steel jobs.

The White House issued Biden’s statement as he campaigns in Michigan and Wisconsin, two Midwestern industrial strongholds that are crucial for him to win in November. Presumptive Republican nominee Donald Trump is vying for the same blue-collar workers in those states as Biden and has pledged to block the deal outright.

Biden moved against the deal as he prepares to host Japanese Prime Minister Fumio Kishida for a White House state dinner on April 10. The US president has looked to Japan as a bulwark against China in the Asia-Pacific region, but his opposition to the deal could strain the two countries’ relationship. 

Read: Cliffs CEO Says His US Steel Deal Is ‘Absolutely Gone’ 

Bloomberg has reported previously that the Biden administration is examining Nippon Steel’s connections to China in its review of the US Steel deal, as it looks to ratchet up pressure on Beijing.

Biden’s comments on Thursday also drive home the influential position of the steelworkers’ union and its president David McCall. Talks between Nippon Steel and the USW have been rocky so far: the union is seeking written guarantees about honoring all labor contracts, while the company is offering at least $1.4 billion in additional capital spending as a sweetener. Nippon Steel has said it will honor all agreements US Steel has with the USW.

Read: US Steel Takeover’s Fate May Hang on the Words of a Union Boss

It’s not clear what impact, if any, Biden’s statement will have on the Cfius review. The Treasury Department did not immediately respond to a request for comment.

Senator Bob Casey, a Pennsylvania Democrat who faces reelection in November, praised Biden for his “commitment to maintaining an American steel industry” but did not explicitly oppose the Nippon Steel sale, only saying he would “work like hell against any deal that leaves our Steelworkers behind.” Some stakeholders have concerns that US Steel might shutter facilities and cut jobs without a capital infusion.

John Fetterman, Pennsylvania’s other Democratic senator, cheered on Biden’s statement, posting “jam this up” on X, formerly Twitter.