The United States Senate is the upper chamber of the United States Congress, which along with the United States House of Representatives—the lower chamber—comprises the legislature of the United States.
The composition and powers of the Senate are established by Article One of the United States Constitution. The Senate is composed of senators, each of whom represents a single state in its entirety, with each state being equally represented by two senators, regardless of its population, serving staggered terms of six years; with 50 states currently in the Union, there are 100 U.S. Senators. From 1789 until 1913, Senators were appointed by legislatures of the states they represented; following the ratification of the Seventeenth Amendment in 1913, they are now popularly elected. The Senate chamber is located in the north wing of the Capitol, in Washington, D.C.
As the upper house, the Senate has several powers of advice and consent which are unique to it; these include the approval of treaties and the confirmation of Cabinet secretaries, Supreme Court justices, federal judges, other federal executive officials, flag officers, regulatory officials, ambassadors, and other federal uniformed officers. In addition to these, in cases wherein no candidate receives a majority of electors for Vice President, the duty falls to the Senate to elect one of the top two recipients of electors for that office. It further has the responsibility of conducting trials of those impeached by the House. The Senate is widely considered both a more deliberative and more prestigious body than the House of Representatives due to its longer terms, smaller size, and statewide constituencies, which historically led to a more collegial and less partisan atmosphere.
Article I, Section 3, of the Constitution, sets three qualifications for senators: (1) they must be at least 30 years old; (2) they must have been citizens of the United States for the past nine years or longer; and (3) they must be inhabitants of the states they seek to represent at the time of their election. The age and citizenship qualifications for senators are more stringent than those for representatives. In Federalist No. 62, James Madison justified this arrangement by arguing that the "senatorial trust" called for a "greater extent of information and stability of character."
The Senate (not the judiciary) is the sole judge of a senator's qualifications. During its early years, however, the Senate did not closely scrutinize the qualifications of its members. As a result, three senators who failed to meet the age requirement were nevertheless admitted to the Senate: Henry Clay(aged 29 in 1806), Armistead Thomson Mason (aged 28 in 1816), and John Eaton (aged 28 in 1818). Such an occurrence, however, has not been repeated since. In 1934, Rush D. Holt Sr. was elected to the Senate at the age of 29; he waited until he turned 30 (on the next June 19) to take the oath of office. In November 1972, Joe Biden was elected to the Senate at the age of 29, but he reached his 30th birthday before the swearing-in ceremony for incoming senators in January 1973.
The Fourteenth Amendment to the United States Constitution disqualifies from the Senate any federal or state officers who had taken the requisite oath to support the Constitution, but later engaged in rebellion or aided the enemies of the United States. This provision, which came into force soon after the end of the Civil War, was intended to prevent those who had sided with the Confederacy from serving. That Amendment, however, also provides a method to remove that disqualification: a two-thirds vote of both chambers of Congress.