The Presiding Officer of the United States Senate is the person who presides over the United States Senate and is charged with maintaining order and decorum, recognizing members to speak, and interpreting the Senate's rules, practices, and precedents. Senate presiding officer is a role, not an actual office. The actual role is usually performed by one of three officials: the Vice President; an elected United States Senator; or, in special cases, the Chief Justice. Outside the constitutionally mandated roles, the actual appointment of a person to do the job of presiding over the Senate as a body is governed by Rule I of the Standing Rules.
The Vice President is assigned the responsibility by the Constitution of presiding over the Senate and designated as its president. The vice president has the authority (ex office, for they are not an elected member of the Senate) to cast a tie-breaking vote. Early vice presidents took an active role in regularly presiding over proceedings of the body, with the president pro tempore only being called on during the vice president's absence. During the 20th century, the role of the vice president evolved into more of an executive branch position. Now, the vice president is usually seen as an integral part of a president's administration and presides over the Senate only on ceremonial occasions or when a tie-breaking vote may be needed.[1]
The Constitution also provides for the appointment of one of the elected senators to serve as President pro tempore. This senator presides when the vice president is absent from the body. The president pro tempore is selected by the body specifically for the role of presiding in the absence of (as the meaning of pro tempore, literally "for the time being") the actual presiding officer. By tradition, the title of President pro tempore has come to be given more-or-less automatically to the most senior senator of the majority party. In actual practice in the modern Senate, the president pro tempore also does not often serve in the role (though it is their constitutional right to do so). Instead, as governed by Rule I, they frequently designate a junior senator to perform the function.
When the Senate hears an impeachment trial of the President of the United States, by the procedure established in the Constitution, the Chief Justice is designated as the presiding officer.
