The senator elected to preside over the chamber in the absence of the Vice President.
The U.S. Constitution specifies three legislative leadership positions. First is the Speaker of the House, and second is the Vice President, who serves as president of the Senate. Third is the Senate President Pro Tempore, which receives the least attention of the three. Despite the role's relative lack of notoriety, it is third in the presidential line of succession, behind the Vice President and the Speaker of the House, respectively. The "President Pro Tem," as the position is commonly known, also receives security protection from the Capitol Police (due to succession considerations) and a larger salary than other senators.
The President Pro Tem is elected by his or her peers in the Senate. Since 1945, it has been the senator from the majority party who has served in the Senate the longest (thus not necessarily the senator with the longest tenure overall). The President Pro Tem typically serves in this position until a new majority takes over the chamber or the senator retires, whichever comes first.
The Vice President is technically responsible for many of the core day-to-day operations of the Senate, such as deciding points of order, enforcing decorum in the chamber, recognizing senators to speak, and signing bills. But due to the Vice President's frequent absence, the President Pro Tem assumes these duties. In turn, the President Pro Tem often delegates the more mundane duties to junior members of the majority party (i.e., what qualifies as grunt work for a U.S. senator).
Can You Ever Forgive Me?
To date, 90 individuals from 39 states have held the office. Recent Presidents Pro Tem include Robert Byrd (D-WV), Ted Stevens (R-AK), Daniel Inouye (D-HI), Patrick Leahy (D-VT), and Orrin Hatch (R-UT), the current President Pro Tem. The upcoming 116th Congress will be one of major transition, and the changes will reverberate all the way up the Senate ladder.
Senator Hatch is retiring at the end of the year, with 2012 GOP presidential nominee Mitt Romney replacing him. Despite Romney's high public profile, he will not inherit any of Hatch's seniority and will join the Senate as one of its most junior members alongside eight other incoming freshmen senators. Come January, Senator Grassley (R-IA) will be the longest-serving member in the Senate majority and is expected to be elected the next President Pro Tem. Alongside this new responsibility, Senator Grassley is also slated to take over Hatch's chairmanship on the powerful Senate Finance Committee.
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