Within states congressional district boundary lines are drawn by the state legislatures. All House members are elected in single-member districts, the total number of which has been set by Congress at 435. Today, each House member has about half a million constituents. House members are elected every 2 years. The Constitution awards each state two senators.
Incumbency is important in congressional elections.
A high proportion of members of Congress seek reelection, and an overwhelming proportion of them succeed. Still, the turnover of the congressional membership is high because of deaths and retirements, because some run for other offices, and, increasingly, because some do not win reelection. Both houses of Congress are organized into majority and minority political parties, each with its own leadership, but the House and the Senate are organized differently. In the House the leader of the majority party serves as the Speaker, who is the presiding officer of the House. Because the Speaker controls debate in the House, has an important role in the selection of committee members and chairpersons, and can influence the scheduling and dispensation of legislation, the Speaker possesses substantial power.