GOP congressional leaders have stood aside the past four months as President Donald Trump has attacked legislative branch prerogatives — shuttering agencies, canceling federal grants and imposing sweeping tariffs.

Now he’s meddling in their actual back yard.

A White House push to seize control of the Library of Congress over the past week has run temporarily aground due to quiet but firm resistance from Speaker Mike Johnson and Senate Majority Leader John Thune, according to three people granted anonymity to describe the sensitive situation.

While they have not challenged Trump’s abrupt firing last week of Librarian of Congress Carla Hayden, they have questioned his power to name an acting successor and other library officials, including the nation’s top copyright official. That opposition has left Trump’s intended leader for the library, Deputy Attorney General Todd Blanche, in at least temporary limbo.

Asked Wednesday who is in charge of the library, Thune said, “I'm not sure that's been determined.”

Johnson said in a brief interview that Trump “clearly has the authority to remove a Librarian of Congress” but acknowledged questions about filling the vacancy: “We want to make sure all the — you know, everything's followed correctly.”

The top leaders’ equivocal answers leave open the possibility that Blanche, previously Trump’s personal lawyer, could soon take control of the world’s largest library and its 162 million cataloged items, more than 3,200 employees and 1.6 million yearly visitors. Thune said Blanche’s team met Tuesday with staff from the Senate Rules and Administration Committee, which oversees the library, and “worked through some of the issues and questions that we had concerns about.”

“So I don't know, officially … whether he's in there yet or not," Thune added.

In a subsequent interview Wednesday, Thune said “consultations” are ongoing and that he expects “more discussions about it next week." That’s also when the president and his top aides are expected back from a Middle East trip and could weigh in.

The dispute over the library’s leadership has emerged as a fresh test for the separation of powers — and for how far Republicans on Capitol Hill will let Trump go when their own prerogatives are on the line. It’s especially stark given that the library, located across the street from the Capitol, is where lawmakers get their research, enjoy elegant dinners, host meetings and escort visitors into the ornate Reading Room. That’s not to mention its name.

“It’s the Library of Congress, after all, not the library of the president,” said Sen. Alex Padilla of California, the top Rules Committee Democrat. He is among numerous congressional Democrats who are raising alarms about a potential Trump takeover of the library and what it could mean.

Sen. Chris Van Hollen (D-Md.) called the attempted takeover “obviously a violation of separation of powers” and one he hoped “would finally cause Senate Republicans to respond.” Sen. Richard Blumenthal (D-Conn.) called it “like a thumb in the eye to Congress.”

Beyond the concerns about interbranch relations, lawmakers and staff are anxious about potential White House access to and preservation of congressional data — including confidential dealings with the Congressional Research Service.

For now, Robert Randolph Newlen, who was Hayden’s top deputy, remains in charge as acting chief librarian. But Trump has acted to make changes deeper in the library ranks, also dismissing Registrar of Copyrights Shira Perlmutter over the weekend.

Two officials arrived Monday at the library’s Madison Building and sought to enter the premises, identifying themselves as Blanche’s deputies: Brian Nieves — a deputy chief of staff and senior counsel in Blanche’s office, who has been designated acting assistant librarian — and Paul Perkins — an associate deputy attorney general and veteran Justice Department attorney, who has been named acting registrar of copyrights and director of the Copyright Office.

The two men were turned away after library officials challenged the legitimacy of their appointments — a determination that came with tacit backing from congressional leadership offices. Newlen told library employees Monday that Congress had not offered explicit “direction” on “how to move forward” following Hayden’s dismissal.

Some rank-and-file Republicans are openly questioning how much control Trump or any president ought to have over an arm of Congress.

“If they are congressional employees, and I know that there's a discussion on that, then they belong to Congress and not to the executive branch,” said Sen. Mike Rounds (R-S.D.), who sits on the subcommittee that funds the Library of Congress.

Under federal law, the president is empowered to nominate the librarian of Congress subject to Senate confirmation. But the library’s authorizing statute, which sets out a 10-year term for the top official, is silent on how they might be fired or replaced in an interim capacity.

The White House asserts that Trump has the authority to name an acting chief who can serve temporarily under the Federal Vacancies Reform Act, like any other federal agency with a presidentially appointed and Senate-confirmed leader.

But many lawmakers on Capitol Hill insist the Vacancies Act does not apply to an arm of the legislative branch. “It's clear the acting librarian is in charge,” Padilla said Tuesday, referring to Newlen.

Thune said it might not be so clear-cut, referring to the president's nominating power and the institution's "hybrid" nature combining its library functions and its oversight of copyright. The copyright office issues regulations, something the courts consider to be executive branch activity.

“It's unusual," he said that there needs to be further clarity “on those issues where there is that kind of overlap, but I think at least for now there's just a concern that the congressional legislative branch equities are protected."

Padilla met Tuesday with Rules Chair Mitch McConnell (R-Ky.) and said that Thune and Minority Leader Chuck Schumer “are part of the conversation as well.”

Thune told reporters earlier this week that congressional leaders were “not entirely” consulted before the White House began its purge. That might have been an understatement: The top House lawmakers overseeing the Library of Congress found out about the firings while on a trip together to Nashville.

Reps. Bryan Steil (R-Wis.) and Joe Morelle (D-N.Y.), the respective chair and ranking member of the Committee on House Administration, were meeting with music industry representatives about artificial intelligence issues and enjoying live music at the iconic Bluebird Cafe when they learned of Hayden’s ouster. They broke the news to the group at a Friday morning roundtable focused on copyright just hours before Perlmutter was terminated as copyright chief.

Congress has previously acted to claw back control of a congressional arm from the White House, moving in 2023 to end the president’s power to nominate the architect of the Capitol and instead keep hiring and firing power solely in the legislative branch. Morelle is now proposing something similar for the Library of Congress, and several Democrats are speaking up in support.

“It's not the president's librarian, it's Congress's librarian,” said Sen. Amy Klobuchar (D-Minn.), who authored the legislation dealing with the architect of the Capitol.

Jordain Carney, Meredith Lee Hill, Lisa Kashinsky and Nicholas Wu contributed to this report.