Article 1, Section 6, Clause 1
Charles Pinckney, Breach of Privilege, Senate5 Mar. 1800Annals 10:72, 74
The remainder of the clause respecting privilege is so express on the subjects of privilege from arrest, government of members, and expulsion, that every civil officer in the United States, and every man who has the least knowledge, cannot misunderstand them. I assert that it was the design of the Constitution, and that not only its spirit, but letter, warrant me in the assertion, that it never was intended to give Congress, or either branch, any but specified, and those very limited, privileges indeed. They well knew how oppressively the power of undefined privileges had been exercised in Great Britain, and were determined no such authority should ever be exercised here. They knew that in free countries very few privileges were necessary to the undisturbed exercise of legislative duties, and those few only they determined that Congress should possess; [Volume 2, Page 338] they never meant that the body who ought to be the purest and the least in want of shelter from the operation of laws equally affecting all their fellow citizens, should be able to avoid them; they therefore not only intended, but did confine their privileges within the narrow limits mentioned in the Constitution.
. . . Let us inquire, why the Constitution should have been so attentive to each branch of Congress, so jealous of their privileges, and have shewn so little to the President of the United States in this respect. . . . No privilege of this kind was intended for your Executive, nor any except that which I have mentioned for your Legislature. The Convention which formed the Constitution well knew that this was an important point, and no subject had been more abused than privilege. They therefore determined to set the example, in merely limiting privilege to what was necessary, and no more.
The Founders' Constitution
Volume 2, Article 1, Section 6, Clause 1, Document 21
The University of Chicago Press
Annals of Congress. The Debates and Proceedings in the Congress of the United States. "History of Congress." 42 vols. Washington, D.C.: Gales & Seaton, 1834--56.