When the Senate is sitting on an impeachment trial, the motions that senators may make are derived, explicitly and implicitly, from its standing Impeachment Rules. For example, Rule V stipulates that senators may approve “orders, mandates, writs, and precepts…and…make and enforce such other regulations and orders in the premises as the Senate may authorize or provide.”
Rule XIX also acknowledges senators’ ability to make motions during an impeachment trial. It requires them to put all questions for witnesses, managers, and counsel, as well as all motions and orders, in writing before sending it to the presiding officer. (Note: Motions to adjourn are exempted from this requirement.)
Rule VI authorizes the Senate to “enforce obedience to its orders, mandates, writs, precepts, and judgments, to preserve order, and to punish in a summary way contempt’s 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.” The rule empowers the Sergeant at Arms to “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.”
Rule XIII sets the schedule for all impeachment trials. It stipulates, “The hour of the day at which the Senate shall sit upon the trial of an impeachment shall be (unless otherwise ordered) 12 o’clock pm.” The provision “unless otherwise ordered” references senators’ ability to make motions to adjust the schedule. Similarly, Rule XXVI clarifies that “the Senate may, by any order adopted without debate, fix a day and hour for resuming such consideration.”
A simple-majority decides all of these motions. The Impeachment Rules do not allow senators to debate during open sessions of a trial. However, Rule XX allows any senator to make a motion to go into closed session. Once the Senate is in a closed session, the rules allow senators to participate in limited debate. Yet even in closed session, all motions decided by a simple majority.