President pro tempore

The president pro tempore of the Senate, often just called the "pro tem," is the officer who presides over the Senate when the vice president, who is its constitutional president, is not present. The title means "for the time being." Article I, Section 3 of the Constitution provides for the office.

By custom since 1945, the Senate has elected the majority party's most senior member to the post. In practice the role is mostly ceremonial, and the pro tem rarely presides, delegating the duty to junior senators of the majority party in rotation. Responsibilities include administering oaths, signing enrolled bills and serving as a member of some commissions, and the pro tem holds a salary slightly higher than other senators.

The pro tem is third in the line of presidential succession, after the vice president and the Speaker of the House. That means the position carries real importance in contingency planning even though its day-to-day influence is limited compared with the majority leader. During an impeachment trial of the president, the Chief Justice presides rather than the pro tem or vice president, a rule that avoids a conflict of interest.