In Gravel v. United States, 408 U.S. 606 (1972), a United States senator acquired copies of classified, top secret documents known as the Pentagon Papers. 408 U.S. at 609, 92 S. Ct. at 2619. After calling a meeting of a Senate subcommittee, the Senator read aloud portions of the Papers and then placed the entire study into the record. 408 U.S. at 609, 92 S. Ct. at 2619. As a result, a federal grand jury began a criminal investigation of the release and publication of the documents. 408 U.S. at 608, 92 S. Ct. at 2618. Subpoenas were issued to an aide of the Senator and to an officer of the private publisher. 408 U.S. at 608, 92 S. Ct. at 2618. The Senator then intervened in the matter and opposed questions based on privilege. 408 U.S. at 608, 92 S. Ct. at 2618. The Gravel court agreed that the Clause prevented questioning of the senator as to his conduct at hearings, his motives in revealing the contents of the papers, and his communications with his aides. 408 U.S. at 616, 92 S. Ct. at 2622. In addition, immunity shielded the congressional aides to the same extent that a lawmaker would be privileged had the lawmaker done the act himself. 408 U.S. at 622, 92 S. Ct. at 2625.