The US Justice Department's third-ranking official plans to step down to work in the private sector, sources say, at a time when President Donald Trump has taken aim at senior law enforcement officials.
Rachel Brand was next in line to Deputy Attorney-General Rod Rosenstein for oversight of Special Counsel Robert Mueller's investigation into potential collusion between Trump's 2016 presidential campaign and Russia and whether the Republican president has sought to obstruct the ongoing probe.
Rosenstein oversees Mueller's investigation because Attorney-General Jeff Sessions recused himself from the matter last year.
After just nine months in her role, Brand had grown increasingly uncomfortable with Trump's escalating attacks on the Justice Department and the FBI, which she and other law enforcement professionals feared was beginning to undermine the rule of law, according to sources.
The attacks have escalated as Republicans in Congress criticised the handling by the Justice Department, FBI and Federal Intelligence Surveillance Court of warrants for surveillance of a Trump campaign adviser, Carter Page, who had ties to Russia.
Brand's resignation was first reported by the New York Times. A source said she was going to work as an executive at retailer Walmart.
A Justice Department spokesman declined to comment.
The news comes a week after Trump approved the release of a classified memo by congressional Republicans that portrays the Russia investigation as a product of political bias against Trump at the FBI and Justice Department.
Trump has also criticised Sessions for recusing himself.
On February 2, just hours before Trump approved the memo's release, Sessions praised Rosenstein and Brand, saying they "represent the kind of quality and leadership that we want in the department".
The FBI's deputy director, Andrew McCabe, stepped down in January after Trump repeatedly criticised him on Twitter.