Sen. Chuck Grassley (R., Iowa), chairman of the Senate Judiciary Committee, has told Deputy Attorney General Rod Rosenstein that he is worried about acting FBI Director Andrew McCabe's independence.

Grassley sent a letter to Rosenstein on Thursday about McCabe's potential conflicts of interest, Politico reports. Grassley expressed concerns about whether McCabe should have recused himself from the investigation into Hillary Clinton's private email server.

McCabe's wife, Jill, received substantial donations from Gov. Terry McAuliffe (D., Va.), when she ran for a seat in the Virginia state senate. McAuliffe was also a top bundler for Hillary Clinton's presidential campaign. The Justice Department's inspector general is investigating whether McCabe should have recused himself, a fact Grassley brought up in his letter.

Grassley also mentioned a gender discrimination complaint against the FBI. Fired National Security Adviser Michael Flynn wrote a letter on behalf of the accused agent; Grassley suggested this may have thrown McCabe's discretion in the FBI's investigation into Flynn into question.

"That evidence and the failure to recuse calls into question whether Mr. McCabe handled the Flynn investigation fairly and objectively, or whether he had any retaliatory motive against Flynn for being an adverse witness to him in a pending proceeding," Grassley wrote.