To maintain the appropriate ordering of the legislative process in the Senate, the Constitution provided for the appointment of a temporary presiding officer when the Vice President was absent from the body. As with Article I, Section 2, Clause 5, vesting the appointment of the Speaker and other officers in the House of Representatives, this clause avoids any inference that the Appointments Clause (Article II, Section 2, Clause 2) might apply to legislative officers. It is, in other words, another carefully drafted provision to protect the separation of powers.

At first, the Senate elected a President Pro Tempore each time the Vice President absented himself from the chair, the office ending upon the return of the Vice President. In 1792, John Adams began the custom of vacating the presidential chair shortly before the end of each day’s session, permitting the Senate to elect a President Pro Tempore who would be in place in case the Vice President died or assumed the functions of the President of the United States. The Senate codified that practice by resolution in 1876.

In 1890, the Senate adopted the procedure that continues today of electing a President Pro Tempore who holds the office until replaced. By custom, the Senate elects the Member of the majority party who is senior in terms of length of service. By statute, the office is third in succession to the presidency after the Vice President and the Speaker of the House of Representatives.

The President Pro Tempore is not a legislative leader. He supervises the Senate and makes procedural rulings while in the chair. Like the Vice President, the President Pro Tempore does not actually preside over many sessions of the Senate. He appoints substitutes from the Members to sit in the chair when he steps down. Often the daily roster of substitutes includes younger Senators in order to acquaint them with the procedures of the Senate. Unlike the Vice President, the President Pro Tempore does not vote to break tie votes, but rather votes as a Senator from his own state.

When there was no Vice President because of death or succession to the Presidency, the President Pro Tempore occupied the “office” of the Vice President to oversee the Senate staff and to perform the other administrative duties of the Vice President, but he did not thereby succeed to the constitutional office of the Vice President.

In recent decades, the Senate has created the ceremonial office of Deputy President Pro Tempore, available to Senators who were former Presidents or Vice Presidents. Hubert Humphrey is only person to have held the post under those terms (though Senator George Mitchell was given the post while President Pro Tempore John Stennis was ill). In addition, the Senate has established the honorary position of President Pro Tempore Emeritus for a senator of the minority party who had earlier served as President Pro Tempore.

“Other Officers” of the Senate include the majority and minority leaders who have the primary responsibility of directing the flow of legislation, party secretaries, the Sergeant at Arms and Doorkeeper, Chaplain, Secretary of the Senate, Chief Clerk, and Executive Clerk.