The election of members of Congress is as important to the people of the United States as the election of the president. This article describes the composition of the U.S. Congress, the factors that come into play in congressional elections, and the possible impact of the 2008 elections on U.S. government policy. L. Sandy Maisel is a professor of government at Colby College in Waterville, Maine.

When citizens throughout the United States go to the polls on November 4, 2008, they will be voting not only for president but also for all 435 members of the House of Representatives and for one-third of the United States Senate. Attention will be focused on the presidential election, but the congressional elections are equally important.

In the system of government established by the U.S. Constitution, the executive and legislative branches share in decision making. Separation of powers would not be important if the same party always controlled the presidency and the Congress and if party members were disciplined in following their leaders. Neither is the case. The governing powers are separated not only in the sense that the two elected branches of the federal government are populated with different individuals — i.e., no U.S. senator or representative may serve simultaneously in the executive branch — but also in that those serving in office are chosen in separate elections, though the elections are held on the same day. Citizens have the option to vote for a president from one party, a senator from another, and a member of Congress from either of those or a third party. It is not only possible, but common, for one political party to control the White House and the other party to control one or both branches of the Congress. This situation is called "divided government." Moreover, members of Congress and senators are not dependent on party leaders for reelection and often express that independence by voting for the interests of their constituents even when they differ from party positions.

Makeup of the Congress

Congress has two bodies: the House of Representatives and the Senate. The House was meant to be the body closest to the people, popularly elected from relatively small districts with frequent elections (every two years). Today California, the most populated state, has 53 seats in the House of Representatives. The seven most sparsely populated states have one each.

The Senate was designed to reflect state interests. Each state, regardless of population, has two senators. Senators serve six-year terms, staggered so that one-third of the Senate seats are up for reelection every two years. Originally, senators were chosen by state legislatures, but since 1913 they have been popularly elected. The founders thought that the senators would be removed from popular passion because they were indirectly elected for longer terms; many question whether that is the case today.

Though the Senate and the House have equal powers, a Senate seat is generally thought to be more prestigious than a House seat: The constituency is larger (except in the case of the seven smallest states, where it is the same), the term length is longer, and senators receive more national attention because there are fewer of them.

House and Senate elections function under the same rules, with minor variation by state. The Democratic and Republican parties and any other parties active in a state nominate candidates through primary elections; independent candidates achieve a spot on the ballot by petition. The winner of the November general election is the candidate with the most votes; a majority is not needed.

Factors in Electing Members of Congress

There are three basic elements determining congressional elections: partisanship of the district, the presence or absence of an incumbent, and the issues of the day. The U.S. political system has been described as a competitive two-party system; the Democratic and Republican parties have dominated U.S. politics since the middle of the 19th century. More than 99 percent of those elected to the Congress in recent years have been either Democrats or Republicans. A system with single-member districts and plurality winners favors a two-party system. Third-party or independent candidates, who would benefit from a system of proportional representation, gain no benefit from close finishes.

The competition for control of the Congress has been intense in recent decades — just as it has for the presidency. However, the competition is not intense in every district and in every state. Some districts and even some states lean heavily toward one party or the other. For example, Democrats usually win in Massachusetts; Republicans, in Wyoming. Exceptions have occurred, but no politician will enter the 2008 congressional election without knowing the normal partisanship of district or state voters.

Election results can be explained by the presence or absence of an incumbent. For more than three decades, more than 95 percent of those incumbent members of the House of Representatives who have sought reelection have been successful. Incumbent U.S. senators have also been successful in achieving reelection. Even in elections in which many seats switch parties, more partisan turnover comes in seats where no incumbent is running. The effect of these factors is seen when one looks at potential candidates seeking party nominations to run for the House and Senate. In seats likely to be hotly contested — e.g., seats in which no incumbent is running in a district closely divided between Democrats and Republicans — it is likely that many candidates will run in each party's primary. If a seat is open but one party dominates the district, that party's primary is likely to see intense competition, but there will be little or no competition in the other party. Finally, if an incumbent is running, he or she is unlikely to face serious competition, and party leaders in the other party might have to scramble to find anyone to run. Each of these generalizations applies less to the Senate than to the House, because Senate seats are seen as more valuable and fewer election results can be easily predicted in advance.

A new president will be elected in 2008, and national issues — the war in Iraq, terrorism, immigration policy, energy dependence — will dominate the scene. If President Bush's approval rating remains low among voters and these issues are unresolved going into the November election, the Democrats may have an advantage in closely contested races.

Implications for Governance

Following the 2006 congressional elections, Washington was marked by divided government, with the Republicans controlling the White House and the executive branch and the Democrats controlling both houses of the Congress, though by a razor-thin margin in the Senate.

The Republicans currently hold 22 of the 34 Senate seats that will be contested in 2008. Even slight Democratic gains will not give that party an overwhelming Senate majority. Senate rules require 60 votes to take major action; the Democrats are extremely unlikely to approach that number.

The Democrats hold approximately 30 more House seats than do the Republicans. While many incumbents' plans remain in flux, approximately 25 representatives are likely to vacate their seats after this Congress. Most of those seats — and perhaps another 25, many held by Democrats who took over Republican seats in 2006 — will be hotly contested in 2008. The Democrats seem to have a slight advantage in these races and might add slightly to their majority, but again not enough to give them a free hand in governing.

As a result of the upcoming congressional elections, if a Republican is elected president in 2008, he may face a determined opposition that controls a majority of both houses of Congress. If a Democrat is elected, he or she is likely to govern with a Congress controlled by his or her party, but one in which the Republicans retain enough strength to thwart major policy initiatives.

A governing system with separation of powers, significant checks and balances, and the majority of legislative election outcomes determined by incumbent strength, not national trends, fosters slow change in national policy. That is what the authors of the Constitution intended. Critical issues will dominate the 2008 election. While on some issues the new president will be able to act without congressional concurrence, on many more, the policies of the U.S. government, if not the rhetoric, will change only slightly.

The opinions expressed in this article do not necessarily reflect the views or policies of the U.S. government.