<P> The President pro tempore of the United States Senate ( often shortened to 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 the President of the Senate ( despite not being a Senator ) , 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>
when does the president pro tempore of the senate preside
During the Vice President 's absence