When Trump wanted to fire then-FBI Director James Comey, who was overseeing the Russia probe, Rosenstein wrote the memo that the White House used to justify the dismissal. But eight days later, Rosenstein took a step that Trump feared would end his presidency: appointing Robert Mueller as special counsel.
Earlier Thursday, the Senate voted 54-45 to confirm the veteran government official, mostly along party lines. Barr, who also served as attorney general from 1991 to 1993 during President George H.W. Bush's administration, succeeds Jeff Sessions.
Rep. Jerrold Nadler, D-N.Y., says he is holding the vote "in an abundance of caution" to ensure that acting Attorney General Matthew Whitaker appears and "answers our questions cleanly."