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United States senators are typically ranked by the length of their tenure in the Senate. Each state is represented by two senators. The senator in eachU.S. state with the longer time in office is known as thesenior senator; the other is thejunior senator. This convention has no official standing, though seniority confers several benefits, including preference in the choice ofcommittee assignments, physical offices, and the member's choice of desk in rare occasions. When senators have been in office for the same length of time, a number of tiebreakers, including previous offices held, population of their state, and alphabetical last names are used to determine seniority. By tradition, the longest serving senator of the majority party is namedpresident pro tempore of the Senate, the second-highest office in the Senate and the third in theline of succession to the presidency of the United States.^[1]

TheUnited States Constitution does not mandate differences in rights or power, but Senate rules give more power to senators with more seniority. Generally, senior senators will have more power, especially within their owncaucuses.

There are several benefits, including the following:

• Traditionally, the most senior member of the majority party is namedpresident pro tempore of the Senate.
• Senators are given preferential treatment in choosingcommittee assignments based on seniority. Seniority on a committee is based on length of time serving on that committee, which means a senator may rank above another in committee seniority but be more junior in the full Senate. Although the committee chairmanship is an elected position, it is traditionally given to the most senior senator of the majority party serving on the committee, and not already holding a conflicting position such as chairmanship of another committee. Theranking member of a committee (called the vice-chairman in someselect committees) is elected in the same way.
• Greater seniority enables a senator to choose a desk closer to the front of theSenate Chamber.
• Senators with higher seniority may choose to move into better office space as those offices are vacated.^[2]
• Seniority determines the ranking in theUnited States order of precedence.

The beginning of an appointment does not always coincide with the date the Senate convenes or when the new senator is sworn in.^[3]

In the case of senators first elected in a general election for the upcoming Congress, their terms begin on the first day of the new Congress. For most of American history this was March 4 of odd-numbered years, but effective from 1935 the20th Amendment moved this to January 3 of odd-numbered years.

In the case of senators elected in arun-off election occurring after the commencement of a new term, or a special election, their seniority date will be the date they are sworn in and not the first day of that Congress. A senator may be simultaneously elected to fill a term in a special election and elected to the six-year term which begins on the upcoming January 3. Their seniority is that of someone chosen in a special election.

The seniority date for an appointed senator is usually the date of the appointment,^{[citation needed]} although the actual term does not begin until they take the oath of office. An incoming senator who holds another office, including membership in theU.S. House of Representatives, must resign from that office before becoming a senator. In the 1970s, some senators would resign a few days or weeks early so that their successor may be appointed to the seat and have greater seniority than other freshmen. In 1980, party rule changes removed seniority advantages in such cases.^[4][3]

A senator's seniority is primarily determined by length of continuous service; for example, a senator who has served for twelve years is more senior than one who has served for ten years. Because several new senators usually join at the beginning of a new Congress, seniority is further determined by prior federal or state government service and, if necessary, the amount of time spent in the tiebreaking office. These tiebreakers in order are:^[3]

1. Former senator
2. Formervice president of the United States
3. Former member of theUnited States House of Representatives
4. Former member of theCabinet of the United States
5. Former stategovernor
6. Population of state based on the most recentcensus when the senator took office

When more than one senator had such office, its length of time is used to break the tie. For instance,Jerry Moran,John Boozman,John Hoeven,Ron Johnson,Rand Paul,Richard Blumenthal, andMike Lee all took office on January 3, 2011. The first two senators mentioned had served in the House of Representatives: Moran had served for fourteen years and Boozman for nine. As a former governor, Hoeven was ranked immediately after the former House members. The rest were ranked by population as of the2000 census. These ranked from 27th to 33rd in seniority when the119th United States Congress convened.

If two senators are tied on all criteria, the one whose surname comes first alphabetically is considered the senior senator. This happened withJon Ossoff andRaphael Warnock, both of Georgia, who were sworn in on January 20, 2021. Because they were both newly elected senators from the same state, with no prior government service, no other tie-breaking criteria could be used. The Senate's official records, as well as the Democratic Caucus, thus consider Ossoff, whose name comes first alphabetically and who had been elected to a full six-year term, as the senior senator.^[3][5][6]

Only relevant factors are listed below. For senators whose seniority is based on their state's respective population, the state population ranking is given as determined by the relevantUnited States census current at the time that they began service.^[7][8]

The most senior senators by class are Maria Cantwell (D-Washington) from Class 1, Mitch McConnell (R-Kentucky) from Class 2, and Chuck Grassley (R-Iowa) from Class 3. Cantwell is the most senior senator from her class while being the junior senator from her state.

  Republican(53)     Democratic(45)     Independent(2)

• List of current United States senators
• List of United States Senate committees
• Seniority in the United States House of Representatives
• List of members of the United States Congress by longevity of service

• Lists of United States senators by seniority

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