The presidency has thrived because of the broad powers conferred on it by the Constitution. Some incumbents have interpreted these powers expansively, often with congressional and judicial acquiescence.

The executive-power clause of Article II, Section 1, states merely that "The executive Power shall be vested in a President of the United States of America." The scope of this clause was disputed in George Washington's presidency when he promulgated (1793) his proclamation of neutrality in the French Revolutionary Wars. Rejecting the argument that the clause was merely a statement of fact, Washington agreed with Alexander Hamilton that it was a grant of power and that the direction of foreign policy is inherently an "executive" function residing in the presidency.

A constitutional power to which presidents have given vast scope is the commander-in-chief power (Article II, Section 2). One of the freest interpretations of this power was exercised by Lincoln, who - after the Civil War erupted, and while Congress was not in session - called up 75,000 men and waged war for 12 weeks, relying on his independent authority. Lincoln claimed to possess the "war power," which, he said, combined the commander-in-chief power with the president's duty "to take care that the laws be faithfully executed."

The commander-in-chief power has been cited to justify commitment of the armed forces to scores of short-term hostilities. A far more ambitious military intervention occurred in Vietnam. Critics contended that the Vietnam War could be legally sustained only by a congressional declaration of war, which was never made.

Although the Constitution specifies that the president can make treaties, the requirement that they be approved by a two-thirds vote of the Senate has often driven presidents to use executive agreements instead. If congressional appropriation or other action is required, only a majority vote is necessary. The term executive agreement is not in the Constitution. For authority to make such agreements presidents cite the executive-power clause and the commander-in-chief power. Bill Clinton invoked presidential emergency powers early in 1995 to provide a $20-billion bailout loan to Mexico, thereby circumventing Congress.

Presidents have, by constitutional interpretation, enlarged their powers in relations with Congress. Early presidents, for example, employed the veto only when they considered legislation unconstitutional, but Jackson extended it to legislation he considered objectionable on policy grounds, as presidents have continued to do. After Congress appropriates funds, the president may impound them, or delay their expenditure, usually to correct some deficiency of procedure or policy. But President Richard Nixon enormously expanded the practice by impounding billions of dollars of appropriations. Subsequently, both the judiciary and Congress acted to limit the president's power to impound appropriations.

Tenure of office confers power. Presidential tenure is protected by a rigorous impeachment procedure. Conviction requires a two-thirds vote of the senators present. President Andrew Johnson escaped conviction by a single vote. In 1974, President Nixon, facing impeachment and almost certain conviction, became the first president to resign. President Ford, exercising the president's pardoning power, pardoned Nixon for all federal crimes that he "committed or may have committed or taken part in." Clinton was the second president to be impeached (in December 1998), but the House vote was largely partisan and he won acquittal by a comfortable margin in the Senate (Feb. 12, 1999).

Executive Privilege. Presidents also claim to possess executive privilege, or the right to withhold information from Congress and the public. Although the term executive privilege was not used until the 1950s, George Washington in effect employed it in denying executive papers regarding Jay's Treaty (1794) to the House of Representatives. Other presidents also invoked the doctrine, but Eisenhower expanded it substantially in denying executive papers and testimony to Sen. Joseph McCarthy's investigation of Communist infiltration of the government. In court proceedings concerning Watergate, President Nixon sought to withhold tapes and transcripts of White House conversations, but in United States v. Richard M. Nixon (1974) the Supreme Court ruled that executive privilege did not immunize him from judicial proceedings. President Clinton also invoked executive privilege to prevent some of his aides from testifying during Kenneth Starr's grand jury investigation of the so-called Whitewater matter. The courts disallowed the claim.

Presidential Power and the Supreme Court. It should be noted that although the Supreme Court of the United States determines presidential power by its interpretation of the Constitution, the Court has seldom directly checked the exercise of presidential power. In many cases, the Court has affirmed it. In United States v. Curtiss-Wright Export Corporation (1936), for example, the Court acknowledged a broad presidential power to make executive agreements. The Court's rulings against the president have occurred mainly in civil liberties cases, such as Ex parte Milligan (1866), striking down a presidential authorization of the trial of civilians by a military tribunal in an area far removed from the theater of war. In Youngstown Sheet and Tube Company v. Sawyer (1952), Truman's seizure of the steel mills on his own authority was held unconstitutional.

Actual Presidential Use of Power. Like other kinds of power, formal presidential power cannot always be used in all its fullness. Several major factors determine the way presidents exert power at any given time.

A president needs opportunities for using power. If times are quiet and no urgent problems are apparent - as in the America of 1880, for example - even the most dynamic and skillful president cannot use power extensively. Presidents have employed their powers most fully in visible major crises, such as the Civil War and the world wars, and in grave economic emergency such as the Great Depression of the 1930s, when one-fourth of the workforce was unemployed. When crises are less obvious, as in the energy crisis of the 1970s, the president may have difficulty persuading the public and Congress of the necessity for serious action.

The powers presidents can actually employ also depend heavily on their political skills. Some analysts called psychobiographers or psychohistorians stress that how the president uses power is also determined by the president's personality. Personality characteristics may, for example, cause a president to work very hard, but without being attuned to public sentiment. The strivings of these individuals may become so compulsive as to lead to the rigid - and futile - pursuit of a policy. Woodrow Wilson, for example, took an absolute stand on the League of Nations, rejecting compromises that might have saved much of his project in the Senate.

How the president uses power may also depend on the president's own conception of the office. Some presidents, such as James Buchanan or William Howard Taft, have interpreted their powers narrowly, declining to act unless power was specifically granted in the Constitution or in statutes. At the other extreme are the presidents who, like Theodore Roosevelt, feel constrained in their "stewardship" only by what is expressly forbidden by the Constitution.

The Current Issue of Executive Power. After the long, drawn-out, and eventually unpopular Vietnam War and the excesses of Watergate, the presidency passed into an era of criticism and reassessment. The office was seen to have become inordinately powerful and to be threatening civil liberties. It was viewed as having placed the political system in disequilibrium by drawing excessive power to the presidency at the expense of the other branches.

All too often the presidency's power expands by congressional default - by the disinclination of the legislature to deal directly with national problems. The bureaucracy of the executive branch has shown itself incapable of a great deal of initiative; addicted to established routines and averse to new ideas with their accompanying risks of failure, the bureaucracy has preferred to leave innovation to the White House staff. This in turn has perhaps encouraged presidential subordinates to use - and abuse - their power in ways that are symptomatic of the presidency's excesses.

Congress became more assertive after Watergate, passing the War Powers Act and other measures to control presidential abuses. It also created its own Budget Office to sharpen its annual review of the budget. Congress employed the appropriations power to constrain presidential initiatives in foreign affairs, with consequences that could be seen in the chief executive's limited responses to military crises in Angola and Congo (Zaire). Congress enlarged its own retinue of experts on committee staffs, in the General Accounting Office, in the Congressional Budget Office, and in the offices of individual legislators and committees, enhancing its ability to challenge the bureaucracies of the executive departments.

In the late 1970s, however, public sentiment began to call for a more assertive presidency that could provide greater leadership to a fragmented and interest-ridden Congress and that could act decisively on the array of stubborn problems that troubled Americans. President Jimmy Carter's inability to guide many of his legislative initiatives through Congress weakened his administration, as did his perceived failure to provide effective action in the Iranian hostage crisis. Carter's successor, Ronald Reagan, who won two landslide election victories, was notably more successful in getting Congress to do his bidding, especially in the areas of increased military spending and tax reform. However, the Reagan administration stumbled into the Iran-contra affair. In effect, the appropriations process was bypassed, a grave violation of the Constitution.

Reagan's successor, George Bush, continued his conservative policies but was forced to allow tax increases in order to lower the budget deficit. In foreign affairs, Bush was the beneficiary of the collapse of communism in Eastern Europe and the disintegration of the USSR, and he mobilized the alliance that defeated the Iraqis in the Persian Gulf War. However, voters perceived him as too engaged in foreign affairs, and his successor, Bill Clinton, accordingly pressed an agenda that included reform of welfare and health care. Although initially successful in pressing his initiatives - notably in lowering the budget deficit and securing ratification of the North American Free Trade Agreement - Clinton failed to deliver on the main promises of his campaign, and, perceived as waffling in both domestic and foreign policy matters, he suffered a stinging rebuff at the polls in the midterm elections of 1994. His zeal in promoting aggressive fund-raising policies to finance the 1996 presidential campaign fueled his reelection but led to harsh criticism of lapses in ethical standards and allegations of the corrupting influence of foreign money - chiefly Asian - on the administration and the party national committee. A Democratic White House and a Republican-controlled Congress nevertheless reached a compromise accord on welfare reform, ongoing deficit reductions, and a future balanced budget. In 1998, President Clinton was able to announce a budget surplus for the first time in 30 years. However, his presidency was soon engulfed in the investigation that led to his impeachment at the end of that year. Following his acquittal (February 1999), it was unclear whether he would be able to work with Congress for the remainder of his term. In fact, Congress gave scant support to Clinton's conduct of the Kosovo war, and the U.S. Senate failed to ratify the Comprehensive Test Ban Treaty, its first rejection of a major treaty since Woodrow Wilson's League of Nations debacle in 1919-20. On the other hand, Congress did approve the Clinton-backed normalization of trade relations with China (2000).

The presidential election of 2000, pitting George W. Bush (son of the former president) against Clinton's vice-president, Al Gore, was one of the closest and most bitterly contested in U.S. history. It was followed by a legal battle over the vote count in Florida that lasted for more than a month, with the U.S. Supreme Court eventually deciding in favor of Bush. He was the first candidate in more than a century to win the presidency while losing the popular vote.