The Justice Department sued a onetime close friend and aide to the first lady, Melania Trump, on Tuesday to try to recoup the profits from a tell-all book that disclosed embarrassing details about her, the third lawsuit in recent months where the department has taken on a White House antagonist.
The decision to file the lawsuit raised new questions about whether President Trump is using the powers of the Justice Department to settle personal scores that have little to do with the federal government.
The aide, Stephanie Winston Wolkoff, wrote in her book, “Melania and Me: The Rise and Fall of My Friendship With the First Lady,” that Mrs. Trump was selfish and image-obsessed, had a strained relationship with her stepdaughter Ivanka Trump and was largely unfazed by her husband’s insults and lewd comments about women.
The Justice Department alleged in the suit that Ms. Winston Wolkoff violated a nondisclosure agreement she had signed with the government when she agreed to volunteer to help Mrs. Trump in the early months of the administration. The pact forbade her from disclosing confidential details she learned during her time working for the first lady, the lawsuit said.
“Defendant Wolkoff has been, and will continue in the future to be, unjustly enriched in the amount of profits, advances, royalties and other advantages resulting from publicity given to the unauthorized disclosures contained in her book,” according to the suit.
The lawsuit takes a broad view of the government’s powers over the rights of former employees. Though it is routine for national security officials to sign agreements not to disclose classified information, Ms. Winston Wolkoff had no access to such material and the private conversations and internal deliberations she described were akin to the kinds of accounts that former aides in many White Houses go on to disclose in memoirs.
The Justice Department said the administration had standing to bring the suit. “This was a contract with the United States and therefore enforceable by the United States,” said Kerri Kupec, a department spokeswoman.
A lawyer for Ms. Winston Wolkoff said in a statement that “this lawsuit is entirely meritless.”
“It represents an effort by the Trumps to enlist the D.O.J. to pursue entirely personal goals and interests,” said the lawyer, Lorin L. Reisner. “The position staked out in the lawsuit also violates the First Amendment.”
The government was likely to face several obstacles because Ms. Winston Wolkoff’s First Amendment rights may override the Trump administration’s pursuit of retribution for her book, according to legal experts.
Some of the Justice Department’s arguments pushed the limits of government secrecy, said Heidi Kitrosser, a professor of law at the University of Minnesota Law School and an expert in constitutional law and government secrecy. She pointed to the government lawyers’ attempt to portray Mrs. Trump as if her conversations were protected by executive privilege.
“These are the types of arguments that are traditionally made about keeping secrets between the president and his advisers,” not first ladies, Ms. Kitrosser said. “Even in the presidential context, courts have found that the president does not have unlimited right to keep secrets.”
She also said the Justice Department appeared to be following Mr. Trump’s years of suing former employees.
“It seems to be consistent in the attitude that manifests itself in N.D.A.s that Donald Trump had former employees and volunteers sign,” Ms. Kitrosser said. “This just steps further by extending it to the first lady’s office.”
In recent months, the Justice Department has taken a series of actions related directly to matters that involve embarrassing disclosures about the president.
The department sued Mr. Trump’s former national security adviser John R. Bolton in June, accusing him of violating nondisclosure agreements as a condition of receiving access to classified information and seeking to stop him from publishing a damaging book about Mr. Trump. A judge rejected the request but allowed the department to move forward with an effort to instead seize his $2 million advance for the book.
Last month, the Justice Department sought to replace Mr. Trump’s personal lawyers with government ones in a defamation suit against him by the writer E. Jean Carroll, who has publicly accused Mr. Trump of raping her in the 1990s in a department store. Attorney General William P. Barr has defended the move, saying it was routine for the department to take over lawsuits against government officials performing their duties — in this case, Mr. Trump answering reporters’ questions about the news of the day.
Around the time Mr. Trump took office in 2017, he told the White House counsel at the time, Donald F. McGahn II, that he wanted West Wing officials to sign nondisclosure agreements. Mr. McGahn concluded that the agreements would be difficult to enforce but to assuage the president, he directed his office to create wide-ranging agreements intended to stop former officials from discussing their time working for Mr. Trump. Dozens of officials signed the agreements, which were similar Ms. Winston Wolkoff’s.
Mr. Trump’s attempts to translate his practice of requiring nondisclosure agreements into government have had mixed success.
The president’s campaign is in litigation with a former aide, Omarosa Manigault Newman, who signed such an agreement during the 2016 campaign. Two years later, she described Mr. Trump as racist in a book, and the campaign sued.
It has suggested that she could remedy her comments by paying for a $1 million ad campaign that would rebut her statements. Ms. Manigault Newman’s lawyer has described the proposal as “speech with a gun to your head.”
Maggie Haberman and Ben Protess contributed reporting.