Every two years, Americans elect the entire House of Representatives and one-third of the Senate. The two major political parties each seek to gain the majority of seats in both houses of Congress so that they can more easily advance their legislative agendas. Our article takes a look at the process and is then followed by analysis from political expert Thomas E. Mann, who assesses prospects for Republicans and Democrats in this year's congressional elections. Mann is W. Averell Harriman chair and senior fellow at the Brookings Institution in Washington, D.C.

Because each of the three branches of the American government—executive, legislative and judicial—is an equal force in the U.S. system of "checks and balances," whether the Republicans or Democrats control the houses of Congress is of vital importance.

Although the president sets the political agenda for the country, Congress has an enormous influence on whether or not an administration can accomplish its goals. The houses of Congress alone have the power to pass legislation, approve or deny appointments of cabinet department executives, ambassadors and judges, provide oversight of—and investigate—government agencies, ratify treaties, regulate commerce, control taxation and spending policies, declare war and approve funding for the military.

The terms under which the debate on any issue takes place are controlled by the majority party in each house of Congress because it controls the leadership and membership of the various Congressional committees.

Since the November 1994 mid-term elections (the mid-point in a president's four-year term of office), the Republican party has controlled the House of Representatives. The same is true for the Senate, except for a five-month period in 2001 when Republican Senator James Jeffords of Vermont left the Republican party to become an unaffiliated independent, thus moving formal control from the Republicans. For Democrat Bill Clinton, president from 1993-2001, it meant continually adapting his legislative proposals to gain the support of the opposition party controlling Congress; for Republican President George Bush, it has meant a somewhat freer hand to implement his agenda.

The entire House of Representatives, in which the size of a state's delegation is determined by its population, is up for election every two years. Representation in the Senate, on the other hand, is equal for all states—each has two senators, elected for six year terms; only a third of its members are up for election in any two-year election cycle. The vice-president holds the tie-breaking vote in Senate deliberations.

Redistricting is also a factor in Congressional elections. Because the House of Representatives is based on state population, the Congressional districts in each state are usually re-drawn according to the population information obtained in the U.S. census conducted every 10 years. The party holding the majority of seats in each state's legislature at that time controls the redistricting process and often uses that power to draw the new district lines in ways that favor its candidates. This is known as "gerrymandering."

With control of Congress being so vital to enacting the party platform, the political parties necessarily target House and Senate races much as they do presidential races, concentrating on potential voters in "swing" Congressional states or districts where elections are so close they could go to either party. Both parties hope their candidates will have "coat tails"—the ability to entice voters who, because they are enthusiastic about a certain candidate, will vote for the same party's candidates in other races.

Currently, the composition of the Senate is 51 Republicans, 48 Democrats and one independent who tends to votes with the Democrats; and the Republicans have a 229 to 205 majority over the Democrats, with one independent member, in the 435 member House. Even a small shift in these seats in the 2004 general election will have a large impact on the ability of the next president to carry out his promised action plan for American.

Democratic party prospects for gaining majority control of the Senate and House now rest importantly on the performance of its presidential candidate, Senator John Kerry. The increase in straight-ticket party voting in recent years means that competitive congressional races can tip one way or the other depending on the showing of the candidates at the top of the ticket. A comfortable win by Kerry could well provide the margin of victory in several hotly contested Senate races sufficient to enable the Democrats to win a very narrow majority, while a Bush victory makes it more likely that the Republicans will retain or increase their 51-seat majority. Democrats face much longer odds in regaining control of the House. To overtake the Republicans, they need to pick up just 13 additional seats in a 435-seat chamber. However, the historically small number of genuinely competitive races (about three dozen seats, half of which are now held by Democrats) mean they probably need a Kerry landslide to move back into the majority.

Apart from the presidential contest, Republicans have an advantage in the Senate because they are defending fewer seats in more hospitable territory. The competitive terrain in the Senate is limited to 10 of the 34 states with elections this cycle, only two of which feature seriously threatened incumbents. Minority Leader Tom Daschle of South Dakota is locked in a tight battle with former Republican congressman John Thune. And Alaska Senator Lisa Murkowski, appointed by her father, Governor Frank Murkowski, to fill his unexpired term in the Senate, faces a very strong challenge from former Democratic governor Tony Knowles. Democrats must defend five seats in the South where their incumbents have decided to retire: Florida, Georgia, South Carolina, North Carolina, and Louisiana. The Republican candidate is heavily favored in Georgia; Democrats have strong candidates in the four other races but must compete mostly on unfavorable partisan terrain. Republicans are defending open seats in Illinois, Oklahoma, and Colorado. Democrat Barack Obama, who was the keynote speaker at the Democratic convention, is certain to win in Illinois but the others are too close to call.

In the House, Republican prospects have been buoyed by several successful rounds of redistricting, which have sharply reduced the number of competitive seats and given the Republicans a national advantage of at least a dozen seats. The recent mid-decade partisan gerrymander in Texas orchestrated by House Majority Leader Tom DeLay was drawn to give the Republicans an additional half-dozen seats. Absent a strong national tide, they can be expected to hold or modestly increase their present majority.

If George Bush is reelected, he will likely work again with slender Republican majorities in the Senate and House, enough to control the agenda but not to outmuscle filibusters [lengthy speeches aimed at delaying action on legislation] in the Senate or restiveness among Republican moderates in the House. His ambitious agenda for building an ownership society at home and spreading freedom and democracy around the world could face some obstacles on Capitol Hill.

If John Kerry is victorious, he will likely face a House and possibly also a Senate controlled by the Republicans. He would be forced to deal with Republicans in both chambers, which would entail substantial changes in the proposals he is championing in the campaign. But divided party government is more the norm than the exception in contemporary American politics, and the evidence suggests that such governments are more productive and enact more sustainable policies than might be expected.

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

Senate Races to Watch

Of the 34 Senate seats up for election this year, a number of races have sparked unusual interest and coverage in the United States. Some of these races will play a pivotal role in determining which political party will have control of the Senate. While the Democrats seek to retake the Senate, the Republicans aim to expand their current 51-49 majority.