Since the beginning of the Republic, American presidents have vied with the other branches of government for power. And in times of war and national emergency, presidents have exercised heightened levels of authority in some cases openly sidestepping the Constitution to do what they felt was necessary.
In the larger battle for power, America's 43rd president, George W. Bush, seems no different.
What is different, say experts on presidential power, is that the open-ended nature of Mr. Bush's "war on terrorism" is fast creating new realities of executive power, with no firm expiration date. Some question whether the exigencies of preventing future terror attacks are fundamentally and permanently tipping the constitutional balance of power to the president's advantage.
"It is one thing to hold your breath for a couple of years and hope the administration isn't going to abuse its power ... but this is probably going to go a lot longer than any war we've ever had," says Louis Fisher, a separation-of-powers expert at the Congressional Research Service.
In fighting the war on terror, the Bush administration has taken a series of measures consolidating presidential power. These include cutting back on civil liberties, bolstering White House secrecy, and announcing a new foreign-policy doctrine that highlights preemptive action over international cooperation and diplomacy.
SOME scholars believe this reach for power is both necessary and justified in a world of terrorists seeking weapons of mass destruction.
"We are so vulnerable. We cannot bulletproof this country," says Robert F. Turner of the Center for National Security Law at the University of Virginia Law School. Some curtailment of civil liberties may be necessary to safeguard the nation, he continues: "It may well be that 10 people are having to spend a year or two in confinement in order to save 10,000 people from being murdered."
Others see lurking dangers in an approach that emphasizes the president's ability to act quickly, decisively, and secretly often at the expense of constitutional safeguards aimed at preventing abuses of power.
"Caution lights should be flashing here," says presidential scholar Allan Lichtman of American University in Washington. "The presidency is gaining power in a way that makes it yet more remote for control by the public and by Congress."
American history is filled with examples of power struggles between the executive and legislative branches. Less frequent are examples of the courts playing a decisive role in reining in a president who has exceeded his legal authority.
"The purpose of the Constitution was not only to grant power, but to keep it from getting out of hand," former Supreme Court Justice Robert Jackson observed in a 1952 case in which the high court ruled that President Truman had no legitimate power as commander in chief to take over US steel mills during the Korean War.
"Such power either has no beginning or it has no end. If it exists, it need submit to no legal restraint," Justice Jackson wrote. "I am not alarmed that it would plunge us straightway into dictatorship, but it is at least a step in that wrong direction."
AMERICAN presidents have sometimes ignored constitutional mandates when, in their view, compliance might harm the nation. Jefferson believed he violated the Constitution by acting alone and in secret while arranging the Louisiana Purchase from France.
Likewise, Lincoln acted without the necessary congressional approval when he issued the Emancipation Proclamation. Lincoln also acted unconstitutionally at the dawn of the Civil War, when he suspended habeas corpus and allowed citizens to be held without trial, in an effort to keep Confederate sympathizers from blocking Union troops as they moved south to defend Washington.
And during World War II, President Roosevelt and the US Supreme Court endorsed the mass internment of Japanese Americans in an action now widely recognized as unconstitutional.
President Bush's actions, in contrast, are relatively minor, according to some experts who say his proactive approach to preventing terrorism is motivated more by fear than by the desire to accumulate power. "I think there is genuine worry that things may come unraveled on their watch if there is another [terrorist] incident," says Tom Henriksen, a senior fellow at the Hoover Institution on War, Revolution, and Peace in Stanford, Calif.
Others see a more opportunistic, power-hungry White House.
"The Imperial Presidency" is a phrase made famous by historian Arthur Schlesinger Jr. in his book about US presidential power from the beginning of the Republic through Richard Nixon. The collapse of the Nixon presidency and the Vietnam War devastated the executive branch, leading to such limits as the War Powers Resolution of 1973, which restricts the president's power to commit troops abroad without congressional approval. It also led to strict congressional oversight and other restrictions on the FBI and CIA.
After Nixon, presidents could only dream of the power that FDR enjoyed, when first the Great Depression and then World War II spawned far-reaching new executive-branch functions. Roosevelt also had both houses of Congress on his side for all of his 12-year tenure.
Power is "a goal for Bush and [Vice President] Cheney," says Larry Sabato, a professor of government at the University of Virginia. "The belief among some scholars, and certainly occupants of the executive branch, is that since Vietnam and Watergate, executive power has been trimmed too much and that executive prerogatives have been eliminated."
The first President Bush believed in this strongly, and that's where Mr. Cheney got it, says Mr. Sabato. "So Bush Jr. is taking up where Bush Sr. left off."
The implications extend far beyond US borders, analysts say.
"The United States has more power than any nation or empire in the history of the world. More than the Ottoman Empire or the Roman Empire," Mr. Lichtman says. "Nobody doubts that we can win a war anywhere. The issue is, can military power do what needs to be done not, can we exercise military power."