The United States Senate, according to the United States Constitution, (Article I), is required to choose a President pro tempore (or, "president for a time," often shortened to President pro tem), who presides over the Senate in the absence of the Vice President. Because of the smaller size of the Senate and because Senate rules of procedure give more power to individual senators, the President pro tem is not a powerful position especially in comparison to the Speaker of the House of Representatives or even the party leaders of the Senate. As of April 3, 2005, the current President pro tempore of the Senate is Ted Stevens of Alaska.
The President pro tempore is a constitutionally mandated office of the Senate, equivalent to the Speaker of the House of Representatives, except that the Speaker wields far greater political power. Most power rests with party leaders and individual senators. The President pro tempore represents the Senate at formal events and, in the absence of the Vice President, presides over the Senate and, with the Speaker of the House, over joint sessions of Congress. Due to the high visibility of joint sessions, they are one of very few instances in modern times where the Vice President does make an effort to attend and preside, so Presidents pro tempore rarely have the opportunity to preside at a joint session.
The President pro tempore, together with the Speaker of the House, is the authority to which declarations of presidential inability are transmitted in accordance with the 25th Amendment to the Constitution.
The President pro tempore is third in the line of presidential succession, following the Vice President and the Speaker of the House.
History
Originally, the President pro tempore was appointed on a daily or weekly basis when the Vice President of the United States was not present to preside over the Senate. Until the 1960s, it was common practice for the Vice President to preside over daily Senate sessions, so the President pro tempore rarely presided over the Senate unless the Vice Presidency became vacant.
Until 1891, the President pro tempore only served until the return of the Vice President to the chair or the adjournment of a session of Congress. Between 1792 and 1886, the President pro tempore was second in the line of presidential succession following the Vice President and preceding the Speaker of the House of Representatives. The President pro tempore and the Speaker were removed from succession in 1886, but were restored in 1947. This time, however, the President pro tempore followed the Speaker.
In the early years, the President pro tempore was usually a senator noted for his skill at parliamentary procedure. Over the years, however, the office became less work-a-day and more ceremonial; gradually, it became the custom for it to be given to a senior senator. Since the 1940s it has been the invariable rule that the most senior senator of the majority party holds the office.
The President pro tempore, just like the Vice President, over time has ceased presiding over the Senate on a daily basis, notably due to its lack of power or glamour. Instead, junior senators are designated president pro tempore to preside over the Senate on a daily basis. This allows junior senators to learn proper parliamentary procedure.
Presidents pro tempore of the United States Senate