The Senate president pro tempore is one of our national legisla- ture's three constitutionally mandated officers, along with the vice president and Speaker of the House. The president pro tempore is authorized to preside over the Senate, sign legislation, and issue the oath of office to new senators. Pro Tem: Presidents Pro Tempore of the United States Senate Since 1789 traces the development of the office in four brief essays and features biographical profiles and photographic images of its 87 occupants. Pro Tem offers stories that demonstrate how much the Senate has changed throughout its long history, while striving to maintain the ideals of its 18th-century creators.