It's important to understand that the FBI's power was very asymmetric.

J Edna Hoover could assign a team to gather kompromat on a person and to surveil them or harass them.

A Congressperson has no equivalent ability to threaten the Director of the FBI. At best, they could spread a rumor, but a rumor doesn't catch fire when journalists / editors had too high of ethics to repeat unverified rumors.