ALTHOUGH CONGRESS CONSTITUTES a single branch of the U.S. government, the House of Representatives and the Senate are distinct bodies. Each has its own powers, rules, practices, and traditions. Some of the most apparent and important differences between the two concern the membership of these bodies. For example, the practice of having representatives serve for two years and senators for six has remained the same since it was established by the founders in the Constitution. All House members face reelection every two years, but Senate terms are staggered so that only one-third of the senators face reelection at the same time. To run for election, a representative must be twenty-five years old and a resident of his or her state for at least seven years. A senator must be thirty and a resident for nine years.

Another obvious difference...