He will also help oversee the special counsel investigation into Russian election interference and possible ties to the Trump campaign as well the inquiry into Michael D. Cohen, Mr. Trump’s longtime personal lawyer, which is being conducted by federal prosecutors in Manhattan.
Mr. Benczkowski has told lawmakers that he supported Mr. Mueller’s investigation but would not promise to recuse himself from issues involving Russia. Mr. Sessions has stepped back from election-related matters, including the Russia investigation, which is overseen by Rod J. Rosenstein, the deputy attorney general.
Senate Democrats sought to block Mr. Benczkowski’s confirmation, citing a lack of relevant experience. Though he has served in several Justice Department roles — work in legislative affairs and legal policy as well as key leadership posts for the offices of the attorney general, the deputy attorney general and the Bureau of Alcohol, Tobacco, Firearms and Explosives — Mr. Benczkowski was not a federal prosecutor.
“The only apparent qualification that Mr. Benczkowski has is his close relationship with, and political loyalty to, the attorney general and the president,” Senator Patrick J. Leahy, Democrat of Vermont, said in his floor statement during Mr. Benczkowski’s confirmation hearing on Wednesday.
“This could prove to be a historic mistake,” Senator Richard J. Durbin, Democrat of Illinois, warned after Mr. Benczkowski’s confirmation. He, Mr. Leahy and other Democrats on the Judiciary Committee wrote in May to their colleagues urging them to deny Mr. Benczkowski’s appointment.
But 14 former United States attorneys who supported Mr. Benczkowski’s nomination told the Senate that he was a “person of integrity and fairness, and someone whose experience and leadership skills will serve him and the department well.”
Mr. Benczkowski is a “serious attorney” who understands the Justice Department’s importance, said Megan L. Brown, a lawyer at the firm Wiley Rein who worked with him at the Justice Department. “He has a great sense of duty to country and the safety and security of the country, and also understands the seriousness of the threats we face, domestically and abroad,” she said.