When they met, Mr. Trump was ready to talk — but not about the travel ban. His grievance was with Mr. Sessions: The president objected to his decision to recuse himself from the Russia investigation. Mr. Trump, who had told aides that he needed a loyalist overseeing the inquiry, berated Mr. Sessions and told him he should reverse his decision, an unusual and potentially inappropriate request.

Mr. Sessions refused.

(snip)

The special counsel’s interest demonstrates Mr. Sessions’s overlooked role as a key witness in the investigation into whether Mr. Trump tried to obstruct the inquiry itself. It also suggests that the obstruction investigation is broader than it is widely understood to be — encompassing not only the president’s interactions with and firing of the former F.B.I. director, James B. Comey, but also his relationship with Mr. Sessions.