[Mackubin Thomas Owens is professor of national security at the Naval War College.]

IN JUNE of 1863, Abraham Lincoln wrote a letter to Erasmus Corning, who had sent him the resolutions of the Albany Democratic convention censuring the Lincoln administration for what it called unconstitutional acts, such as military arrests of civilians in the North. This letter remains the best articulation of the problems that a democratic republic faces when confronted by a crisis that threatens the very existence of that republic.

The essence of Lincoln's argument was that certain actions that are unconstitutional in the absence of rebellion or invasion become constitutional when those conditions exists--in other words, "that the Constitution is not in its application in all respects the same in cases of rebellion or invasion involving the public safety, as it is in times of profound peace and public security."

This past Saturday, President Bush issued his equivalent of the Corning letter. In his weekly address to the nation, the president, speaking live from the Roosevelt Room, addressed the failure of the Senate to renew the Patriot Act, which passed that body 98-1 in the wake of 9/11, and forcefully defended his actions in authorizing the National Security Agency "consistent with U.S. law and the Constitution, to intercept the international communications of people with known links to al Qaeda and related terrorist organizations."

He pointed out that the Justice Department and NSA's top legal officials had reviewed the activities permitted under this authorization and that the executive branch had briefed congressional leaders of both parties more than a dozen times on this authorization and the activities conducted under it.

"This authorization is a vital tool in our war against the terrorists," the president said. "It is critical to saving American lives. The American people expect me to do everything in my power under our laws and Constitution to protect them and their civil liberties. And that is exactly what I will continue to do, so long as I'm the president of the United States."

The president faces a dilemma that was expressed by James Madison in a letter to Thomas Jefferson: "It is a melancholy reflection that liberty should be equally exposed to danger whether the government have too much or too little power." Lincoln addressed this dilemma during his speech to a special session of Congress after Fort Sumter. "Is there," he asked, "in all republics, this inherent, and fatal weakness? Must a government, of necessity, be too strong for the liberties of its own people, or too weak to maintain its own existence?"

THROUGHOUT THE HISTORY of the American republic, there has been a tension between two virtues necessary to sustain republican government: vigilance and responsibility. Vigilance is the jealousy on the part of the people that constitutes a necessary check on those who hold power, lest they abuse it. As Thomas Jefferson wrote, "[I]t is jealousy and not confidence which prescribes limited constitutions, to bind those whom we are obliged to trust with power."

But while vigilance is a necessary virtue, it may, if unchecked, lead to an extremism that incapacitates a government, preventing it from carrying out even its most necessary and legitimate purposes, e.g. providing for the common defense. "Jealousy," wrote Alexander Hamilton, often infects the "noble enthusiasm for liberty" with "a spirit of narrow and illiberal distrust."

Responsibility, on the other hand, is the prudential judgment necessary to moderate the excesses of political jealousy, thereby permitting limited government to fulfill its purposes. Thus in Federalist 23, Alexander Hamilton wrote that those responsible for the nation's defense must be granted all of the powers necessary to achieve that end. Responsibility is the virtue necessary to govern and to preserve the republic from harm, both external and internal. The dangers of foreign and civil war taught Alexander Hamilton that liberty and power are not always adversaries, that indeed, the "vigor" of government is essential to the security of liberty.

President Bush, like Lincoln before him, has taken actions that reflect his agreement with this principle. Due to the unprecedented nature of the emergency created by the threat of catastrophic terrorism, Bush has no choice but to exercise broad executive power.

Bush's critics have of course, accused him of "shredding the Constitution" in the war on terrorism. But as Harvard's Laurence Tribe, certainly no Bush administration cheerleader, has observed, "civil liberties are not only about protecting us from government. They are also about protecting our lives from terrorism." As Justice Jackson famously said of the Bill of Rights, the Constitution "is not a suicide pact."

THOSE WHO CRITICIZE BUSH fail to make an important distinction that Lincoln illuminated in the Corning letter:

I can no more be persuaded that the Government can constitutionally take no strong measures in time of rebellion, because it can be shown that the same could not lawfully be taken in time of peace, than I can be persuaded that a particular drug is not good medicine for a sick man, because it can be shown not to be good for a well one. Nor am I able to appreciate the danger apprehended by the meeting [of the New York Democrats] that the American people will, by means of military arrest during the Rebellion, lose the right of Public Discussion, the Liberty of Speech and the Press, the Law of Evidence, Trial by Jury, and Habeas Corpus, throughout the indefinite peaceful future, which I trust lies before them, any more than I am able to believe that a man could contract so strong an appetite for emetics during temporary illness as to persist in feeding upon them during the remainder of his healthful life.

The means to preserve the end of republican government are dictated by prudence, which according to Aristotle is, the virtue most characteristic of the statesman. Prudence is concerned with deliberating well about those things that can be other than they are (means). In political affairs, prudence requires the statesman to be able to adapt universal principles to particular circumstances in order to arrive at the means that are best given existing circumstances. For Bush, as well as for Lincoln, preserving republican liberty requires the executive to choose the means necessary and proper under the circumstances.

IN TAKING THE STEPS he believes to be necessary to preserve republican government, it is important to note that the president possesses his own inherent constitutional powers. The presidency is not, as one commentator suggested, merely "a kind of independent agency under the ultimate control of Congress." The president is the commander-in-chief, which directly bestows upon him powers in times of military crisis that are not derivative of any congressional power. One of these powers is the prerogative.

THE AMERICAN FOUNDERS and the architects of the Constitution were intimately familiar with the works of the 17th century British philosopher John Locke, so much so that he has been called "America's philosopher." According to Locke, the prerogative is "the power [of the executive] to act according to discretion for the public good, without the prescription of the law and sometimes even against it." Since the fundamental law that the executive ultimately must implement is to preserve society, it is "fit that the laws themselves should in some cases give way to the executive power, or rather to this fundamental law of nature and government, viz. that as much as may be, all members of society are to be preserved."

The prerogative is rendered necessary by the fact that laws arising from legislative deliberation cannot foresee every exigency. For the safety of the republic, the executive must retain some latitude for action. A case in point was Lincoln's actions in the wake of the attack on Fort Sumter, to call up volunteers, declare a blockade of Southern ports, and suspend habeas corpus in some areas. Bush's actions regarding domestic surveillance of terrorists are of the same cloth.

Of course, prudence dictates that the prerogative be exercised rarely, i.e. only during the most dire emergencies. As Lincoln observed in his letter to Corning, what is applicable during time of war is not during a time of peace.

Today, once again we face the perennial tension between vigilance and responsibility as the United States is the target of those who would destroy it. In all decisions involving tradeoffs between two things of value, the costs and benefits of one alternative must be measured against the costs and benefits of the other. At a time when the United States faces an adversary that wishes nothing less than America's destruction, President Bush is correctly taking his bearing from Lincoln, who understood that in time of war, prudence dictates that responsibility must trump vigilance. In response to criticism of his suspension of the writ of habeas corpus, Lincoln asked, ". . . are all the laws but one, to go unexecuted, and the government itself go to pieces, lest that one be violated?" Lincoln's point is as applicable today as it was during the Civil War. If those responsible for the preservation of the republic are not permitted the measures to save it, there will be nothing left to be vigilant about.