But appearing before the Committee on an invitation which is in the nature of a summons, to testify in the investigation originally moved by me into the sale of arms to France, I am obliged to consider my duty as a Senator. Personal inclinations, whatever they may be, cannot be my guide. I must do what belongs to a Senator under the circumstances of the case.
Before answering any questions, I am constrained to consider the competency of the Committee which has summoned me. It is of less importance what these questions may be, although there are certain obvious limitations, to which I will allude at the outset.
The examination of a Senator by a Committee of the Senate on a matter outside of the Senate, and not connected with his public duties, is sustained by precedents,—as when Mr. Seward and Mr. Wilson were examined with reference to the expedition of John Brown;[25] but any examination with regard to his public conduct, and especially with regard to a matter which he has felt it his duty to lay before the Senate in the discharge of his public duties, is of very doubtful propriety. In his public conduct a Senator acts on his responsibility, under sanction of an oath, and the Constitution declares that “for any speech or debate” he “shall not be questioned in any other place.” This inhibition, while not preventing questions of a certain character, must limit the inquiry; but the law steps forward with its own requirements, according to which it is plain that a Senator cannot be interrogated, first, with regard to his conference with other Senators on public business, and, secondly, with regard to witnesses who have confidentially communicated with him.
Referring to the most approved work on the Law of Evidence,—I mean that of Professor Greenleaf,—we find under the head of “Evidence excluded from Public Policy”[26] at least four different classes of cases, which may enlighten us in determining the questions proper for Senators.
1. Communications between a lawyer and client. And are not the relations of Senators, in the discharge of their public duties, equally sacred?
2. Judges and arbitrators enjoy a similar exemption with regard to matters before them.
3. Grand jurors, embracing even the clerk and prosecuting officer, cannot be examined on matters before them.
4. Transactions between the heads of Departments and their subordinate officers are treated as confidential.
Plainly, the conferences of a Senator, in the discharge of his public duties, cannot be less protected.