WASHINGTON (AP) -- President Donald Trump has looked to the marble finishes and hefty price tag of the Federal Reserve headquarters to claim grounds to fire Chair Jerome Powell, with whom he has tussled for years over interest rates. But the extensive use of marble in the building is, at least in part, the result of policies backed by Trump himself.

As the Fed moved forward with plans to renovate its Great Depression-era headquarters in Washington during Trump's first term, it faced concerns in 2020 during a vetting process involving Trump appointees, who called for more "white Georgia marble" for the facade of building.

The Fed's architects said the central bank had wanted glass walls to reflect the Fed as a transparent institution, but three Trump appointees to a local commission felt marble best fit the building's historic character. Marble was added as a result, according to the minutes of the Commission of Fine Arts, which advises the federal government on architecture.

The marble does not explain the roughly $600 million in cost overruns for the Fed headquarters and another nearby office building, now budgeted to cost $2.5 billion, which also includes the addition of an underground parking garage and new glass atria in the building's courtyards. But the roots of its extensive use further muddies the White House's attempts to use the renovation to paint the central banker as profligate spender as a possible pretext to removing him.

"I wouldn't be surprised if the result costs more" because of the added marble, said Alex Krieger, a Harvard University emeritus professor who was a member of the commission and participated in hearings on the Fed's proposal.

Russ Vought, Trump's top budget adviser, cited "premium marble" in a letter to Powell last week as an example of the "ostentatious overhaul."

In a response late Thursday, Powell wrote that the project would "use new domestic marble" for several reasons, including "to address concerns raised by external review agencies."

The National Capital Planning Commission, which also reviewed and approved the Fed renovation project, has started an inquiry into how Powell oversaw the updates.

"The Federal Reserve's extravagant multi-billion dollar renovation happened on the watch of the Fed's leadership, and the Fed's leadership needs to own up for this mismanagement of taxpayer dollars - as well as its botched coverup job," said White House spokesman Kush Desai. A Fed spokesperson declined to comment.

There is an uncomfortable possibility that the fate of the U.S. central bank and its foundational role in the economy hinges on a dispute about renovation costs and architecture, one that could lead a broader legal battle as to whether Trump can dismiss a Fed chair he dislikes after the Supreme Court in May described the institution as having protections against an abrupt firing.

Trump, who has redecorated the Oval Office in gold leaf, has argued that inflation is not a concern, so the Fed can dramatically slash its rate to encourage more borrowing. But Powell and other Fed committee members are waiting to see whether Trump's tariffs lift inflation, which higher interest rates could help blunt.

The Fed chair pushed back against criticism during a June congressional hearing that the renovation was lavish by saying some features were removed due to cost, leading the White House to speculate as to whether Powell deceived lawmakers or made changes to the renovation plans without getting additional approvals. At that hearing, Sen. Tim Scott, R-S.C., also cited "white marble" as an example of extravagance.

James Blair, a White House deputy chief of staff who was recently added to the planning commission, said Wednesday that he would send a letter to the Fed requesting any revisions to the project. His goal is to see whether Powell was accurate in his congressional testimony.

"He's either telling the truth or he isn't," Blair told The Associated Press. "If he's telling the truth, he can prove it by just submitting all the plans and revisions."

Trump said Wednesday that he's "highly unlikely" to try to fire Powell unless there was what he deemed as "fraud."

The attempt to remove Powell before his May 2026 term as chair ends could unleash a devastating financial blowback, as financial markets expect the Fed, with its mission of stabilizing prices and maximizing employment, to be free of White House politicking. The perception that the central bank would use its powers to serve Trump's political ends could lead to higher interest rates on the U.S. debt and mortgages, instead of the declines being promised by the president.

The 115-year old Commission of Fine Arts reviewed the plans for the renovation three times in 2020.

Duncan Stroik, who was appointed to the commission in 2019 during Trump's first term, "proposed an amendment requesting that the next submission include an alternative design in white Georgia marble, the same material used for the five existing buildings along the north side of Constitution Avenue," the minutes of a Jan. 16, 2020, meeting said.

Stroik "does not think the proposed additions defer to the historic buildings as great marble edifices on an important street," the minutes added.

Stroik's amendment was voted down, but the commission didn't fully endorse the Fed's plans. The architects presented new plans in May 2020, though those didn't appear to satisfy Trump's appointees.

Some commissioners "continued to object to the addition as a glass box that is reminiscent of a commercial office building, glowing at night, that would present an unacceptable contrast to the solid masonry architecture of the historic building in its monumental context," the commission wrote in a May 2020 letter to a Fed official.

By July 2020, however, the Fed's architects came back with a new proposal, which included "panels of white Georgia marble" which would be used for the "base, cornice, and other details, consistent with the historic building," the commission's minutes said.

Stroik, now a professor of architecture at the University of Notre Dame, said in an interview that "stone buildings don't necessarily have to cost a fortune." But he acknowledged that the commission had not discussed expenses, which has not been part of its mission.

"If they wanted to play the cost game, you do a marble facade and you do the glass facade and you compare the cost," Stroik said. "And you know, they never did that."

Krieger, the former commission member, noted that the body's discussions became much more contentious after the Trump administration removed several members and replaced them with Stroik and James McCrery, a professor at Catholic University, whom he said often echoed the sentiments in a then- draft executive order from Trump that extolled classical architecture.

"At the time, it was a fierce battle over how literal to the original design should the renovations be," Krieger said. "Normally, that attitude does add costs to the construction project." McCrery declined to comment.

Trump issued the executive order in December 2020, which criticized modernist architecture and expressed a preference for "beautiful" classical buildings with more traditional designs. Biden revoked the order, and Trump reissued it the first day of his second term.

The commission did not fully approve the Fed's project until September 2021, after McCrery and another Trump appointee, Justin Shubow, had been removed by then President Joe Biden.

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Associated Press writer Seung Min Kim contributed to this report.