President pro tempore of the Senate

The Constitution provides that the Senate shall choose a president pro tempore, Latin for for the time being, to preside when the Vice President is absent. In the early republic the Senate elected one only for the duration of each absence. Since 1890 the office has been continuous, and since about 1949 the majority party has given it by custom to its longest-serving senator. Under the Presidential Succession Act of 1947 the president pro tempore is third in line to the presidency, after the Vice President and the Speaker.

In practice the president pro tempore rarely presides. The duty of sitting in the chair through routine sessions is rotated among junior majority senators, a practice that also teaches them the rules. The president pro tempore signs enrolled bills, appoints certain officers and commission members on the recommendation of party leaders, and receives the President's formal notice when invoking the Twenty-fifth Amendment. The office carries additional staff, salary, and a security detail.

Because the post goes to the most senior member, holders have often been among the oldest people in Congress, including Strom Thurmond, who held it at 98, and Robert Byrd. Some have argued that placing a senator chosen purely by seniority third in the line of succession is a constitutional and practical risk, and proposals to change the Succession Act have recurred without success. Chuck Grassley, first elected to the Senate in 1980, became president pro tempore in January 2025.