Congressional elections - Elections to Congress take place every two years. Congress has two chambers.
The Senate has 100 members, elected for a six year term in dual-seat constituencies (2 from each state), with one-third being renewed every two years. The group of the Senate seats that is up for election during a given year is known as a "class"; the three classes are staggered so that only one of the three groups is renewed every two years. Until the Seventeenth Amendment to the United States Constitution in 1913, Senators were elected by state legislatures, not the electorate of states.
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