The two houses of Congress resulted from the "Great Compromise" between large and small states reached at the Constitutional Convention in 1787. Membership of the House of Representatives is apportioned according to a state's population, while in the Senate each state has equal representation.

The Constitutions assigns the Senate and House equal responsibility for declaring war, maintaining the armed forces, assessing taxes, borrowing money, minting currency, regulating commerce, and making all laws necessary for the operation of the government. The Senate holds exclusive authority to advise and consent on treaties and nominations.

The Constitution requires that senators be at least 30 years of age, citizens of the United States, and residents of the states from which they are chosen. Originally, the Constitution also provided that state legislatures would elect senators, but in 1913 the 17th Amendment established direct election of senators by the people.

While the House in 1789 immediately opened its doors to the public, the Senate conducted its business in secret session for the first few years, when it met in New York and Philadelphia. Senators expected that they would act primarily as an advisory council to the president, and as a senior body perfecting, by amendment, legislation that "came up" from the House. However, public pressure encouraged the Senate to construct a visitors gallery, which opened in 1795. In 1800, when the federal government moved from Philadelphia to the newly created District of Columbia, both the House and Senate chambers provided public galleries.

By the 1830's, the Senate had attracted the nation's leading political figures and most gifted orators. Daniel Webster, Henry Clay, John C. Calhoun, and other towering figures made the old Senate chamber the chief forum for debating the great national issues of the day. The French observer Alexis de Tocqueville described the Senate he visited as a body of "eloquent advocates, distinguished generals, wise magistrates and statesmen of note, whose language would at times do honor to the most remarkable parliamentary debates in Europe."

During these decades, the Senate tackled the issues of federal authority versus states'rights, and the spread of slavery into the territories. Valiant efforts to achieve compromise eventually failed, and the nation split apart in a bloody Civil War. Southern members resigned from the Senate as their states seceded, and the new Republican party became the majority of the sharply reduced Senate in 1861, just after it had moved into its spacious new chamber in 1859. Following the war, those senators who favored vigorous reconstruction of the Southern states clashed frequently with President Andrew Johnson, who adopted Abraham Lincoln's more lenient policies. Their clashes culminated in the impeachment trail of President Johnson, in the Senate chamber, where the President was spared from removal from office by a single vote.

A series of weak presidents followed Johnson throughout the remainder of the 19th century, allowing the Senate to become the strongest branch of the federal government. Senators argued that the executive should be subordinate to the legislature, and that the president's sole role was to enforce the laws enacted by Congress. By the beginning of the 20th century, the energetic presidencies of Theodore Roosevelt and Woodrow Wilson challenged senatorial dominance, and the balance of power shifted toward the White House. Still, the Senate delivered President Wilson a major blow at the end of his presidency by rejecting the Treaty of Versailles, which ended World War I and created the League of Nations.

At the depths of the Great Depression of the 1930's, the Senate responded enthusiastically to President Franklin D. Roosevelt's New Deal program of recovery, relief, and reform. An unprecedented burst of legislative activity profoundly altered the size, shape, and scope of the federal government.

By 1937, the Senate had broken with President Roosevelt over his proposal to "pack" the Supreme Court, and strong isolationist sentiments limited Roosevelt's international policies. The attack on Pearl Harbor in 1941 brought a sharp shift in public opinion, and senators rallied behind the war effort. The slogan, "politics stops at the water's edge" expressed the new spirit of bipartisanship in American foreign policy.

A major turning point in the Senate's history occurred with the passage of the 1946 Legislative Reorganization Act, which reshaped the committee system and provided the first professional staff for senators and committees. The Cold War brought an increase in legislation, with the expansion of the national defense program, foreign aid, and economic and military assistance to America's allies.

During the 1950's the Senate engaged in sharp debates over civil rights policies, which stimulated lengthy filibusters, but which eventually resulted in passage of the landmark Civil Rights Act of 1964 and Voting Rights Act of 1965. The Senate also divided over American involvement in the war in Vietnam. Although senators overwhelmingly approved the Gulf of Tonkin Resolution in 1964, they later disagreed over its application, and voted for its repeal. Senate concern over increased presidential powers in foreign affairs led to the passage of the War Powers Act of 1973, requiring Congressional notification and approval whenever American troops are sent into combat.

The Watergate burglary and irregularities of the presidential campaign in 1972 led to a Senate investigation chaired by Senator Sam Ervin of North Carolina. Testimony and evidence gathered by Ervin's committee eventually led to the resignation of Richard Nixon as president. Subsequently, the Senate has striven to maintain a balance with the presidency, supporting presidential initiatives while maintaining vigilant oversight over the operations of the executive branch. This is the system of checks and balances which the framers of the Constitution had envisioned, and which has endured for over 200 years of American representative democracy.

Adapted from The United States Senate: 103rd Congress.