A divided government, in the United States or any similarly structured constitutional republic, is one in which the executive authority is vested in a member of a party not in control of the legislative branch. For example, in the 1990s, the Democratic Party, of which President Bill Clinton was the head, held control of the Congress for only the first two years of Clinton's two terms office, resulting in a divided government for six of the eight years of his presidency.
The United States government is structured on the principal of separation of powers, that is, the legislative authority is held by one body &emdash; the Congress &emdash; and the executive authority, or the power to enact, carry out and enforce the laws enacted by the legislature, is held by the executive branch, which is headed by the president, who is both the head of government and the head of state. Laws passed by the Congress are enacted into law when signed by the president, or, upon his disapproval, upon a 2/3 vote of each House of the Congress, called an “override” of the president's veto. The third branch of the government, the judiciary, is composed of the courts, among whose jobs is the responsibility to interpret the laws and determine their consistency with the Constitution. The judiciary is considered to be impartial and disinterested – that is, it is not motivated by partisan issues, at least partially because federal judges are not elected, but appointed for long terms, often for life.
When one party controls the White House and both houses of Congress, the government is “unified” and it's theoretically easy to pass and enact legislation because of the shared goals held by members of the same party. When the opposing party gains control of even one House of Congress, either the Senate or the House of Representatives, it gains the power to bring government to a standstill by virtue of its ability simply to oppose whatever the president's party proposes.
Some people draw the conclusion that the framers of the American Constitution unwittingly established a governmental structure that would become mired in gridlock and stagnation as the composition of the House and Senate shifted every two years. Others cite the antipathy of the framers toward a strong central government, which helps explain why they would construct a government that requires compromise between parties in order to accomplish anything. In order to gain the opposition's support for any legislation, the president's party must negotiate with the opposition, and the opposition will never agree to any measure that's too egregious.
It's been suggested that divided government is undesirable, and that a unified government is preferable. An analysis of American government in the 20th century shows that for the first 55 years of the century, the government was divided for only eight of those years. Additional analysis shows that some of the most successful administrations in the 20th century, such as those of presidents Ronald Reagan and Bill Clinton, were part of divided governments, and some unified governments, such as the Democratic dominance in the second half of the 1930s and the administration of President Lyndon Johnson, led to what many consider to have been extreme governmental excess. Examples of this include the Democratic initiatives of the 1930s that were subsequently declared unconstitutional and many of President Johnson's “Great Society” bills that still cause controversy.
In addition, one of the most dramatic political scandals in American history, the Watergate scandal, occurred during a divided government, and many have suggested that if President Richard Nixon's Republican party had controlled the Congress during that time, the investigations and revelations that led to the president's resignation in the face of inevitable impeachment might never have taken place. Proponents of a divided government suggest that party loyalty and party “discipline” might encourage members of Congress to overlook in a president of their own party behavior that they wouldn't countenance in a president from the opposing party.