Iraq seems to have the imperial presidency in retreat.

Last week the White House accepted Sen. John McCain's proposal to prohibit cruel, inhumane or degrading treatment of enemy combatants. President Bush is under fire for authorizing the NSA's warrantless interception of international phone calls and e-mails that were linked to possible terrorists and that ended or originated in the U.S.

My name has come up for criticism over these issues because of my service in the Justice Department during Bush's first term. I've defended the administration's legal approach to the treatment of al-Qaida suspects and detainees. I cannot address the National Security Agency's program, which remains classified.

But both instances bring up the issue of presidential power in times of war, and I can speak directly to that: The Constitution creates a presidency that is uniquely structured to act forcefully and independently to repel serious threats to the nation.

Let's consider the president's right to start wars. Liberal intellectuals believe that Bush's exercise of his commander-in-chief power has exceeded his constitutional authority and led to a quagmire in Iraq. If only Congress had undertaken the solemn process of declaring war, they have argued, faulty intelligence would have been smoked out, the debate would have produced consensus, and the American people would have been firmly committed to the ordeal ahead.

But they are off the mark.

Neither presidents nor Congress has ever acted under the belief that the Constitution requires a declaration of war before the U.S. can engage in military hostilities abroad. Although this nation has used force abroad more than 100 times, it has declared war only five times: the War of 1812, the Mexican-American and Spanish-American Wars, and World Wars I and II.

Without declarations of war or any other congressional authorization, presidents have sent troops to fight Chinese Communists in Korea, to remove Manuel Noriega from power in Panama and to prevent human rights disasters in the Balkans. Other conflicts, such as the Persian Gulf War, received "authorization" from Congress but not declarations of war.

Critics of these wars want to upend this long practice by appeals to an "original understanding" of the Constitution. The Constitution, however, does not set out a clear process for starting war. Congress has the power to "declare war," but this clause allows Congress to establish the nation's legal status under international law. The framers wouldn't have equated "declaring" war with beginning a military conflict — indeed, in the 100 years before the Constitution, the British only once "declared" war at the start of a conflict.

Further, the Constitution specifies no step-by-step process to govern war-making, yet it is specific every other time it imposes shared power on the executive and legislative branches.

Why no strict war-making process? Because the framers understood that war would require the speed, decisiveness and secrecy that only the presidency could bring. "Energy in the executive," Alexander Hamilton argued in the Federalist Papers, "is a leading character in the definition of good government. It is essential to the protection of the community against foreign attacks."

And, he continued, "the direction of war most peculiarly demands those qualities which distinguish the exercise of power by a single hand."

Instead of specifying a legalistic process to begin war, the framers wisely created a fluid political process in which legislators would use their funding power to control war.

Would outcomes be better if Congress alone began wars? Not necessarily. Congress led us into two bad wars, the 1798 quasi-war with France and the War of 1812. Excessive congressional control can also prevent the U.S. from entering into conflicts that are in the national interest. Most would agree now that congressional isolationism before World War II harmed U.S. interests, and that FDR should have been able to enter the conflict earlier.

We did not win the four-decade Cold War by declarations of war. Rather, we prevailed through the steady presidential application of the strategy of containment, supported by congressional funding of the necessary military forces.

As we confront terrorism, rogue nations and proliferation of weapons of mass destruction, we should look skeptically at claims that radical changes in the way we make war would solve our problems, even those stemming from poor judgment, unforeseen circumstances and bad luck.

John Yoo, a University of California, Berkeley law professor, is the author of "The Powers of War and Peace." He wrote this for the Los Angeles Times.