<Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> The President pro tempore of the United States Senate (also president pro tem) is the second - highest - ranking official of the United States Senate . Article One, Section Three of the United States Constitution provides that the Vice President of the United States is, despite not being a U.S. Senator, the President of the Senate, and mandates that the Senate must choose a President pro tempore to act in the Vice President's absence . Unlike the Vice President, the President pro tempore is an elected member of the Senate, able to speak or vote on any issue . Selected by the Senate at large, the President pro tempore has enjoyed many privileges and some limited powers . During the Vice President's absence, the President pro tempore is empowered to preside over Senate sessions . In practice, neither the Vice President nor the President pro tempore usually presides; instead, the duty of presiding officer is rotated among junior U.S. Senators of the majority party to give them experience in parliamentary procedure . </P> <P> Since 1890, the most senior U.S. Senator in the majority party has generally been chosen to be President pro tempore and holds the office continuously until the election of another . This tradition has been observed without interruption since 1949 . Since enactment of the current Presidential Succession Act in 1947, the president pro tempore is third in the line of succession to the presidency, after the vice president and the Speaker of the House of Representatives and ahead of the Secretary of State . The automatic line of succession applies only to the presidency; the office of Vice President remains vacant until an appointment is made as provided in the Twenty - fifth Amendment to the Constitution . </P>

Who does the president pro tempore replace in the senate