The late Chief Justice William Rehnquist’s Senate confirmation battles in 1971 and 1986 were more intense and political than previously known, according to a newly released FBI file that also offers dramatic new details about Rehnquist’s 1981 hospitalization and dependence on a painkiller.

The FBI file on Rehnquist, released last week under the Freedom of Information Act, reveals that in 1971, as Rehnquist’s confirmation hearings for associate justice approached, the Nixon Justice Department asked the FBI to run a criminal background check on at least two potential witnesses who were expected to testify against Rehnquist. Then-FBI Director J. Edgar Hoover approved the request.