What are the rules for subpoenaing witnesses in a US Presidential Impeachment trial?
What is (or, perhaps the better question is; In past impeachments, what were) the rules for subpoenaing a witness during a Presidential Impeachment trial?
The rules for subpoenas are the same for any impeachment trial.
The Senate determines who (people) and what (documents) to subpoena. The subpoenas are prepared by the Secretary of the Senate and signed by the presiding officer, then served by the Sergeant at Arms using whatever resources are necessary.
Procedure and Guidelines for Impeachment Trials in the United States Senate.
Rules of Procedure and Practice in the Senate When Sitting on Impeachment Trials, pp. 2-3.
VI. The Senate shall have power to compel the attendance of witnesses, to enforce obedience to its orders, mandates, writs, precepts, and judgments, to preserve order, and to punish in a summary way contempts of, and disobedience to, its authority, orders, mandates, writs, precepts, or judgments, and to make all lawful orders, rules, and regulations which it may deem essential or conducive to the ends of justice. And the Sergeant at Arms, under the direction of the Senate, may employ such aid and assistance as may be necessary to enforce, execute, and carry into effect the lawful orders, mandates, writs, and precepts of the Senate.
While the House managers and counsel for the respondent, each, provide a list of witnesses they intend to call, the Senate makes the final determination, because only the Senate has the power to compel attendance.
Attendance: [p. 82]
The Senate has adjourned on occasion to await the attendance of witnesses. The Senate compels the attendance of witnesses and forces obedience to its orders. It can order witnesses to produce papers.
List to be Called: [p. 84]
During the trial of William W. Belknap in 1876, the counsel for the respondent moved that the managers on the part of the House furnish a list of the witnesses that they intend to call.
Whereupon the Senate agreed to the following order:
Resolved, That the managers furnish to the defendant, or his counsel, within four days, a list of witnesses, as far as at present known to them, that they intend to call in this case; and that, within four days thereafter, the respondent furnish to the managers a list of witnesses as far as known, that he intends to summon.
After the list of witnesses and documents has been determined, subpoenas are issued.
Subpenas [pp. 78-79]
In the trial of Secretary of War Belknap in 1876, a witness attempted to withhold certain evidence which he claimed was "privileged communications." The President pro tempore submitted the question to the Senate as to whether the witness should produce the evidence and it was decided in the affirmative.
The Senate discussed on an earlier occasion how the Sergeant at Arms might enforce its subpena. In 1868 during the trial of Andrew Johnson, there was a discussion of the power of the Sergeant at Arms to summon a posse comitatus and finally the following wording was adopted regarding the powers of the Sergeant at Arms:
. . . And the Sergeant at Arms, under the direction of the Senate, may employ such aid and assistance as may be necessary to enforce, execute, and carry into effect the lawful orders, mandates, writs, and precepts of the Senate.
For the form of subpenas see Rule XXV for Impeachment Trials.
Signed by Presiding Officer:
Under a rule of the Senate subpenas or other writs are signed by the Presiding Officer, be he the Vice President or President pro tempore, during session of the Senate for the trial or while on vacation.
On August 3, 1912, during the trial of Judge Robert W. Archbald, Senator Stone, of Missouri, Propounded the following inquiry:
Mr. President, I should like to propound an inquiry. The Presiding Officer, on other words, the Senator who shall preside, I presume is to attach his signature to the subpenas for witnesses. Is that correct?
On response, the President pro tempore directed the Secretary to read the following rule of the Senate:
V. The Presiding Officer shall have power to make and issue, by himself or by the Secretary of the Senate, all orders, mandates, writs, and precepts authorized by these rules, or by the Senate and to make and enforce such other regulations and orders in the premises as the Senate may authorize or provide.
The text of the subpoenas for impeachment trials is fixed by rule.
Rule XXV (in part): [p. 6]
Form of a subpena to be issued on the application of the managers of the impeachment, or of the party impeached, or of his counsel
To ——— ———, greeting:
You and each of you are hereby commanded to appear before the Senate of the United States, on the ——— day of ———, at the Senate Chamber in the city of Washington, then and there to testify your knowledge in the cause which is before the Senate in which the House of Representatives have impeached ——— ———.
Witness ——— ———, and Presiding Officer of the Senate, at the city of Washington, this ——— day of ———, in the year of our Lord ———, and of the Independence of the United States the ———.
Presiding Officer of the Senate.