On Friday Mr. Rosen told investigators from the inspector general’s office about five encounters with Mr. Clark, including one in late December during which his deputy admitted to meeting with Mr. Trump and pledged that he would not do so again, according to a person familiar with the interview.

Mr. Rosen also described subsequent exchanges with Mr. Clark, who continued to press colleagues to make statements about the election that they found to be untrue, according to a person familiar with the interview.

He also discovered that Mr. Clark had been engaging in unauthorized conversations with Mr. Trump about ways to have the Justice Department publicly cast doubt on President Biden’s victory, particularly in battleground states that Mr. Trump was fixated on, like Georgia. Mr. Clark drafted a letter that he asked Mr. Rosen to send to Georgia state legislators, wrongly asserting that they should void Mr. Biden’s victory because the Justice Department was investigating accusations of voter fraud in the state.