Congressional elections, which occur every two years, are the means of determining who serves in the legislative branch of the United States government. The legislature, or Congress, consists of two houses, the House of Representatives and the Senate. Each house has its own electoral procedure.
A Congressional election occurs in every even-numbered year. Members of the House of Representatives serve for a two-year term. As a result, every Congressional election sees all 435 members of the House up for re-election. Each member is elected to represent a particular Congressional district. The number of districts in a state varies depending on the population of the state.
Unlike members of the House of Representatives, Senators serve a six-year term. As a result, only approximately one third of the 100 Senators run for re-election in any given Congressional election. Each state has only two Senators, and only one of the Senators from a state will be running in any Congressional election. Unlike Representatives, who serve a particular district, Senators serve for the entire state. Senate elections are thus statewide.
Prior to the passage of the 17th Amendment to the United States Constitution in 1913, the procedures for electing Senators varied from state to state. The Constitution decreed that Senators be chosen by the state legislature, but many state legislatures decided to allow Senators to be chosen by popular vote. After the Amendment, the election of Senators became part of the larger Congressional election.
Both Senators and Representatives are now elected by popular vote. In most states, whichever candidate wins a plurality of the votes is elected. This means that in some states, in order to win a Congressional election, a candidate need not have won the votes of most of the voters. He or she must simply have gained the largest number of votes out of any candidate. If no candidate wins a clear majority, however, many states initiate runoff elections, in which the highest-performing candidates run against each other.
Congressional elections in most states follow the same or similar procedures. A party usually nominates its incumbent if the party is in office; otherwise, a party primary or party convention selects the candidate. In most districts and states, the Republican and Democratic parties are the main parties, but others may appear on the ballot if they qualify to do so. The rules for ballot inclusion vary from state to state. Once the candidates have been selected, their names are listed on the ballot, allowing voters to pick the candidate of their choice on election day.