The Speech or Debate Clause is a clause in the United States Constitution (Article I, Section 6, Clause 1). The clause states that members of both Houses of Congress
...shall in all Cases, except Treason, Felony and Breach of the Peace, be privileged from Arrest during their attendance at the Session of their Respective Houses, and in going to and from the same; and for any Speech or Debate in either House, they shall not be questioned in any other Place.
The intended purpose is to prevent a President or other officials of the executive branch from having members arrested on a pretext to prevent them from voting a certain way or otherwise taking actions with which the President might disagree.
A similar clause in many state constitutions protects members of state legislatures in the United States. Legislators in non-U.S. jurisdictions may be protected by a similar doctrine of parliamentary immunity.
On June 15, 1971, Senator Mike Gravel (D-Alaska) received a copy of the Pentagon Papers from Ben Bagdikian, an editor at The Washington Post. Over the next several days, Gravel (who was dyslexic) was assisted by his congressional office staff in reading and analyzing the report. Worried his home might be raided by the Federal Bureau of Investigation, Gravel smuggled the report, which filled two large suitcases, into his Senate office, which was then guarded by disabled Vietnam veterans.