WASHINGTON (AP) -- The Justice Department's No. 3 official is planning to step down at a time of turmoil in the agency.

Rachel Brand is leaving for the top legal job at Walmart, friend and former colleague Jamie Gorelick told The Associated Press Friday.

Brand attracted interest because of her potential to assume a key role in the Trump-Russia investigation. The official overseeing special counsel Robert Mueller's investigation, Deputy Attorney General Rod Rosenstein, has been repeatedly criticized by Trump. If Rosenstein had been fired or quit, oversight would have fallen to Brand. That job would now fall to Solicitor General Noel Francisco.

"She felt this was an opportunity she couldn't turn down," Gorelick said. Walmart sought Brand to be head of global corporate governance at the retail giant, a position Gorelick said has legal and policy responsibilities that will cater to her strengths.

"It really seems to have her name on it," Gorelick said.

President and CEO Doug McMillon said Walmart "is fortunate to have a leader of Rachel Brand's stature join the company."

The New York Times first reported the departure, which comes as the Justice Department has been subject to unprecedented attack by President Donald Trump. His broadsides have strained morale at the institution known for its vaunted independence from the White House.

And her departure leaves another vacancy at the Justice Department, which still lacks Senate-confirmed leaders over many of its most important divisions.

Trump, who has openly lamented his inability to influence Justice Department decisions, has stepped up his criticism in recent weeks, fueled by the release of a politically explosive memo alleging the FBI abused its surveillance powers in the Russia investigation.

Brand, who became associate attorney general in May, has kept a relatively low profile and, unlike other top officials, has not been personally targeted by Trump. Attorney General Jeff Sessions praised the "quality and leadership" of Brand and Rosenstein at a Justice Department event last week that focused on human trafficking, which was one of her stated priorities.

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In a statement, Brand said she is proud of the department's accomplishments during her short time there.

"The men and women of the Department of Justice impress me every day," she said.

Brand was also a high-ranking official in the department under George W. Bush. In her current capacity, she oversaw a number of politically challenging areas of the department, including the civil rights, antitrust and civil divisions.

"Rachel has shown real leadership over many important divisions at the department," Attorney General Jeff Sessions said in a statement Friday night in which he congratulated Brand. "She will always remain part of the Department of Justice family."

She had recently pushed Congress to renew a foreign intelligence surveillance program that gives the U.S. government authority to spy on foreigners located outside the country. And she had been vocal about the department's efforts to support students who say their free speech rights are being violated on college campuses.