President Joe Biden and Donald Trump are in agreement: US Steel’s $14 billion sale to Japanese giant Nippon Steel shouldn’t go forward.

The sitting president made his views clear Thursday with a statement from Biden saying "it is vital" for the Pittsburgh steel maker "to remain an American steel company that is domestically owned and operated."

Trump recently promised to block the merger "instantaneously" if he wins this November after avoiding comment on the topic for weeks after it was announced in December.

The arrival of the candidates at their current stance was perhaps inevitable given the heat of election year politics, opposition from unions that both campaigns are trying to court, US Steel’s roots in the swing state of Pennsylvania, and the intensely negative reaction to the idea of selling an iconic American company to overseas owners.

But the end result masked a more complex debate in recent months that saw some allies of the candidates offering initial views that perhaps the deal wasn't all that bad. At least before the political landscape hardened.

Shares of US Steel (X) have fallen by over 15% since the news of Biden's opposition was first reported by the Financial Times on Wednesday afternoon.

Biden's path from 'serious scrutiny' to outright opposition

Biden's statement on Thursday was the latest step in a wary response to the deal that was evident from the beginning.

On Dec. 21, three days after the news dropped, National Economic Adviser Lael Brainard released a statement saying the deal "appears to deserve serious scrutiny" but stopping far short of outright opposition.

Her statement also mentioned the need to wait for an investigation of the deal to be completed, offering notes like "we welcome manufacturers across the world building their futures in America."

That tone was gone in this week’s brief statement that saw Biden saying, "I told our steel workers I have their backs, and I meant it."

The change came following fierce opposition from midwestern Democrats like Sens. John Fetterman and Bob Casey of Pennsylvania and Sherrod Brown of Ohio.

Labor voices like the United Steelworkers, which endorsed Biden in 2020, have also been vocal about opposition to the deal and issued a statement February saying it "received personal assurances that President Joe Biden has our backs."

This week’s statement also came while the president was campaigning in must-win Midwestern states where opposition to the deal is the deepest. The president traveled to Milwaukee on Wednesday and is stopping in Saginaw, Mich., today before returning to Washington.

The statement also notably comes before the results of any investigation, with a review by the Committee on Foreign Investment in the United States (CFIUS) still apparently ongoing.

A more winding process within Trump-world

The progress to "no" in Trump-world was a little more winding. Trump was notably silent on the issue for weeks after the December announcement but with a public debate of sorts among his aides.

One of Trump's leading voices on trade is Robert Lighthizer, his former trade representative who has stayed in his inner circle. Lighthizer represented US Steel and the larger steel industry for years during his time in the private sector and came out against the idea immediately.

"Countries don't let this happen," he said in a Fox Business appearance on Dec. 21, adding, "It matters who owns American industry."

But the appearance was perhaps more memorable for surfacing a level of debate within Trump's orbit.

Lighthizer's interviewer that day was Larry Kudlow, the former director of Trump's National Economic Council, who took a different tack.

"I don't think they're a big factor," he said of the potential deal's impact on Americans, adding "Japan is an ally" before he quickly pivoted to topics where they agreed.

The divide was even starker when it came to Wilbur Ross, Trump's former commerce secretary, who wrote earlier this year in the Wall Street Journal that "there's nothing in the deal from which the U.S. needs defending" and that there is "no real cause for concern other than xenophobia."

But Trump came down clearly on Lighthizer's side of the debate, saying at the end of January after a meeting with the Teamsters that the deal is "so terrible."

The presumptive GOP nominee now regularly brings up the issue during campaign stops and argues that it was the Trump administration that saved the steel industry but Biden is "letting it go."

Ben Werschkul is Washington correspondent for Yahoo Finance.

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