President Trump on Monday named the No. 2 official at the Justice Department and his former personal lawyer to serve as the acting librarian of Congress, initiating a shake-up at the main research library of the legislative branch that prompted an instant revolt among the staff.
Mr. Trump named Todd Blanche, the deputy attorney general who was his lead defense lawyer in his criminal trial in Manhattan last year, to take over from Carla Hayden, the librarian of Congress whom the president abruptly fired late last week.
But staff members at the Library of Congress pushed back, insisting that Congress must have input and refusing to give two other top Justice Department officials whom Mr. Blanche chose for senior positions there access to the agency’s headquarters on Capitol Hill, according to two people familiar with the situation.
The lockout led to a brief standoff across from the Capitol and became the latest flashpoint in a battle over where Congress’s authority ends and the White House’s begins. The people who described it did so on the condition of anonymity because they were not authorized to comment.
Around 9 a.m., the two Justice Department officials arrived at the library’s James Madison Memorial Building and sought access to the U.S. Copyright Office, which is housed there. They brought a letter from the White House declaring that Mr. Blanche was the acting librarian and that he had selected the two men for top roles at the agency.
They were Paul Perkins, an associate deputy attorney general who the letter said would serve as the acting register of copyrights and the director of the Copyright Office, and Brian Nieves, a deputy chief of staff and senior policy counsel who had been designated as the acting deputy librarian. Mr. Trump also fired the previous director of the Copyright Office, Shira Perlmutter, over the weekend, one of the people said.
Staff members at the library balked and called the U.S. Capitol Police as well as their general counsel, Meg Williams, who told the two officials that they were not allowed access to the Copyright Office and asked them to leave, one of the people said.
Mr. Perkins and Mr. Nieves then left the building willingly, accompanied to the door by Ms. Williams. The library’s staff is recognizing Robert Newlen, the principal deputy librarian who was Dr. Hayden’s No. 2, as the acting librarian until it gets direction from Congress, one of the people familiar with the situation said.
In a brief email to the staff on Monday, Mr. Newlen noted that the White House had named a new acting librarian and suggested that the matter was still unresolved.
“Currently, Congress is engaged with the White House, and we have not yet received direction from Congress about how to move forward. We will share additional information as we receive it,” he wrote, signing the note as the “acting librarian of Congress.”
The librarian of Congress is a presidentially appointed post, subject to confirmation by the Senate.
Representative Joseph D. Morelle of New York, the top Democrat on the House Administration Committee and a member of the Joint Committee on the Library, said the move to fire Dr. Hayden and Ms. Perlmutter amounted to a power grab by the executive branch. He criticized Republicans for not speaking out against it.
“This action once again tramples on Congress’s Article I authority and throws a trillion-dollar industry into chaos,” Mr. Morelle said in a statement after Ms. Perlmutter was fired from the Copyright Office, referring to Article I of the Constitution, which describes the powers of Congress. “When will my Republican colleagues decide enough is enough?”
Mr. Morelle led five other House Democrats in calling for an investigation into whether the library had given the Department of Government Efficiency or other executive branch agencies unauthorized access to congressional or library data.
After Mr. Trump terminated Dr. Hayden, who had served in the job since 2016, the White House accused her of having placed “inappropriate books in the library for children.”
The Library of Congress houses the Congressional Research Service, which provides nonpartisan information to assist in the drafting of legislation, and the Copyright Office, as well as functioning as the nation’s library, holding more than 25 million cataloged books. It is primarily a research facility limited to people 16 years or older, but it also has a children’s reading room.
Tim Balk and Jennifer Schuessler contributed reporting.
