Bureaucratic inaction and the prospect of adopting the intensely politicized Russia investigation were among the reasons Associate Attorney General Rachel Brand quit her high-ranking position at the Justice Department, NBC News reported Monday.

Multiple sources close to Brand told NBC the department's No. 3 official feared the possibility that, for one reason or another, Deputy Attorney General Rod Rosenstein would cede responsibility to her in overseeing the special counsel's investigation into Russian election meddling.

Rosenstein was put in charge of Robert Mueller's investigation following Attorney General Jeff Sessions' decision to recuse himself from the Russia probe. Sessions, a key surrogate for Donald Trump during the 2016 campaign, was found to have previously undisclosed contacts with Russian ambassador Sergey Kislyak that Sessions did not mention in testimony on Capitol Hill.

Reports emerged Friday that Brand planned to leave the department "in the next few weeks." She has accepted a position as Walmart's executive vice president of global governance and corporate secretary, in which she will report directly to the company's President and CEO Doug McMillon.

"We have strengthened our governance capabilities and Rachel will help us continue on that journey," McMillon said Friday. Walmart did not immediately respond to CNBC's request for comment.

Rosenstein has reportedly been the target of Trump complaints lately. Aides have advised Trump not to fire the deputy attorney general.

Sources told NBC that Brand's job change followed a lengthy period of feeling unsupported in her role. As far back as the fall, she expresssed worries to friends about her proximity to the looming Russia investigation, NBC's sources said. Key vacancies in the Justice Department, unfilled more than one year into the Trump administration, exacerbated Brand's discontentment in her position.

About a third of the 13 divisions in Brand's purview, including the civil rights and civil divisions, remain vacant, according to NBC.

The White House and the Department of Justice did not immediately respond to requests for comment.

Read the full report from NBC News.