When a U.S. representative or senator leaves Congress before the end of his or her term, are the people of their congressional district or state left without representation in Washington?

Members of Congress, senators and representatives, usually leave office before the end of their terms for one of five reasons: death, resignation, retirement, expulsion, and election or appointment to other government posts.

While the Constitution does not mandate a method by which vacancies in the Senate are to be handled, vacancies can be filled almost immediately by the governor of the former senator's state. The laws of some states require the governor to call a special election to replace U.S. Senators. In states where replacements are appointed by the governor, the governor almost always appoints a member of his or her own political party. In some cases, the governor will appoint one of the state's current U.S. representatives in the House to fill the vacant Senate seat, thus creating a vacancy in the House. Vacancies in Congress also occur when a member runs for and is elected to some other political office before his or her term is over. 

Since Senate vacancies can be filled so quickly and each state has two senators, it is highly unlikely that a state would ever be without representation in the Senate.

Vacancies in the House, however, take far longer to fill. The Constitution requires that member of the House be replaced only by an election held in the congressional district of the former representative.

"When vacancies happen in the Representation from any State, the Executive Authority thereof shall issue Writs of Election to fill such Vacancies." -- Article I, Section 2, Clause 4 of the U.S. Constitution

According to the US Constitution and state law, the governor of the state calls for a special election to replace the vacant House seat. The full election-cycle must be followed including political party nominating processes, primary elections and a general election, all held in the congressional district involved. The entire process often takes as long as from three to six months.

While a House seat is vacant, the office of the former representative remains open, its staff operating under the supervision of the Clerk of the House of Representatives. The people of the affected congressional district do not have voting representation in the House during the vacancy period. They can, however, continue to contact former representative's interim office for assistance with a limited range of services as listed below by the Clerk of the House.

"Legislative Information:
Until a new Representative is elected, the vacant congressional office cannot take or advocate positions of public policy. Constituents may choose to express opinions on legislation or issues to your elected Senators or wait until a new Representative is elected. Mail received by the vacant office will be acknowledged. The staff of the vacant office can assist constituents with general information concerning the status of legislation, but cannot provide analysis of issues or render opinions.

"Assistance with Federal Government Agencies (Casework):
The staff of the vacant office will continue to assist constituents who have cases pending with the office. These constituents will receive a letter from the Clerk requesting whether the staff should continue assistance or not. Constituents who do not have pending cases but require assistance in matters relating to federal government agencies are invited to contact the nearest district office for further information and assistance."