The Trump White House has a new target in its campaign to expand executive power: the Library of Congress. Never mind the name — administration lawyers are now arguing that the main research library of the legislative branch doesn’t actually belong to Congress.

A push to claim the institution as executive turf isn’t a one-off. It’s the latest move in a broad effort by President Trump and his administration to erase the traditional lines that separate the branches of government.

The administration has challenged Congress’s constitutional power of the purse, shrugged off court orders to limit Trump’s powers, and unleashed the US DOGE Service on offices outside the executive branch.

The White House has argued that voters gave Trump a mandate through the 2024 election to exert power in new ways and rein in government spending through new, untested means.

White House press secretary Karoline Leavitt had decried the prior library leadership, referring to books that were not appropriate for children, even though the library does not lend books to children. Individuals cannot borrow directly from the Library of Congress.

“There were quite concerning things that she had done at the Library of Congress in the pursuit of DEI and putting inappropriate books in the library for children,’’ she said in a press briefing, referring to librarian Carla Hayden and diversity, equity, and inclusion programs.

Trump fired Hayden and US Copyright Office director Shira Perlmutter earlier this month as part of a shake-up at the world’s largest library, and sought to name two Justice Department officials to take their place.

The White House declined to respond to questions about the legal claim that the Library of Congress falls under the executive branch and other questions about the separation of powers.

Resistance from a Congress controlled by the Republican Party led by Trump has been limited. But since the power struggle at the library, there have been some rebuffs of Trump’s efforts to assert control over the legislative branch.

Perlmutter is disputing her firing in court. In response to her lawsuit, the administration argued Monday that the Library of Congress is an executive branch entity, and the president can remove Perlmutter through a federal law that sets the rules for presidents to temporarily fill vacant positions that require Senate approval.

Perlmutter disagreed with the administration’s assertion that the Library of Congress is not a legislative branch entity in a filing. An emergency bid to block her firing was rejected by a judge Wednesday, but both sides were told to submit a schedule to continue the litigation.

So far, the acting heads of the library and the copyright office have not been replaced after pressure from lawmakers.

“I think what we’re going to have to do with some of these organizations, like the Library of Congress, GAO, is have Congress appoint the head to make it crystal clear that these are congressional institutions,’’ said Senator Susan Collins, a Maine Republican and chair of the Senate Appropriations Committee.

Anne Joseph O’Connell, an administrative law professor at Stanford Law School, said that the president has some authority via the Vacancies Act over certain positions, including the librarian. However, she said it is the librarian who has the authority to fire the copyright head. She also said that the White House’s claim that the president has inherent Article II authority to name acting officials, if successful in court, “would radically transform executive power.’’

A particular area of concern for Congress is the library’s database of all lawmakers’ research requests, an employee said, which dates back to the 1990s. Those requests were made under a strict promise of confidentiality, another employee said.

The library has always taken its oath of secrecy very seriously, the employee said. Only designated staff can access the database of records requests, which are not visible to the rest of the library, per the employee, and staff are trained not to discuss congressional information requests with anyone but the person making the request.

But the director of the Congressional Research Service can see all of the research requests — and that position is appointed by the librarian, a third staffer noted. So if Trump manages to anoint a handpicked supporter as the next librarian, it could mean someone friendly to the president is able to pore through lawmakers’ queries.

“You can see how this might be concerning to members,’’ the staffer said. “For example, any Republicans … who wrote in with questions about the impeachment processes during the last Trump administration.’’