President pro tempore of the United States Senate
The President pro tempore (/ˌproʊ ˈtɛmpəriː/ or /ˌproʊ ˈtɛmpəreɪ/), also president pro tem, is the second-highest-ranking official of the United States Senate. The United States Constitution states that the Vice President of the United States is the President of the Senate, despite not being a senator, and that the Senate must choose a president pro tempore. Since 1890, the most senior senator in the majority party has generally been chosen to be president pro tempore; this tradition has been observed without interruption since 1949.
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 senators of the majority party to give them experience in parliamentary procedure.
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.
Following the death of Daniel Inouye on December 17, 2012, Patrick Leahy, a Democrat and senior senator from Vermont, was elected to the position by unanimous consent.