To the Editor:

Abraham Sofaer ("The Best Defense?" January/February 2010) argues that when the United States wishes to carry out acts of preventive self-defense or humanitarian intervention that are "technically illegal" under international law, it should seek justification according to a standard of international "legitimacy." But this view underestimates the risks of ignoring legality. For one, gaining legitimacy will prove increasingly difficult if the United States does not have the law on its side.

The trouble stems largely from the problematic wording of the United Nations Charter. Article 2(4) prohibits "the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations." Virtually any use of force arguably violates the territorial integrity or political independence of some state. Hence, Article 2(4) is generally read as a blanket prohibition against using military force across borders, with only two exceptions: when the UN Security Council authorizes it and when it falls under the right of self-defense as outlined in Article 51.

But actual state practice shows that democratic governments do not consider Article 2(4) so constraining. Instead, they have often used force that was justified only by the much broader "Purposes of the United Nations," which are found in Article 1 of the charter and include "the prevention and removal of threats to the peace."

Consider the Cuban missile crisis. When U.S. intelligence discovered the presence of nuclear missiles in Cuba, President John F. Kennedy imposed a naval quarantine and threatened to sink Soviet vessels headed for the island. The Soviets protested that these threats violated Article 2(4) -- which was correct under the provision's generally accepted meaning. Yet Kennedy pushed ahead.

Ignoring Article 2(4), most free governments at the time applauded Kennedy's approach, and it has borne the color of legitimacy ever since. But those governments were heavily dependent on Washington. Had they not been, they might have withheld their support and left the United States with neither legality nor legitimacy on its side. The United States would have been painted as an international outlaw for taking necessary actions to prevent and remove grave threats to the peace -- actions entirely consonant with the purposes of the UN.

International law matters, and the United States has a great interest in stable rules that command international adherence. Democracies depend on sustained political support at home and abroad for the success of their war strategies. This makes politics a limiting factor in the strategic power of democratic states. And because international law often defines the terms of political debate, it follows that strategic power often depends on international law. Indeed, questions of legality set the stage for the diplomatic debacle that the United States suffered in the months before the Iraq war -- a debacle that almost undermined the entire war effort.

Sofaer's approach -- giving up on stable rules in the hope of winning legitimacy on a case-by-case basis -- entails significant risk. It would mean relying on political support from other governments just when that support is getting more elusive -- and important -- due to post-Cold War multipolarity and the rise of new powers with interests of their own. In a world of increasingly diverse and diverging strategic interests, legality will become even more important for marshaling political support at home and abroad. Unless the United States has legality on its side to begin with, the fountain of legitimacy is bound to dry up.

Sofaer acknowledges that international law should change and makes several good suggestions to that end. One is to judge the legality of military actions according to the purposes of the UN. This means construing narrowly Article 2(4)'s clause on "territorial integrity or political independence," in accordance with both the purposes of the UN and actual state practice. Laying the foundations for this change should be a priority for U.S. diplomats.

Weapons of mass destruction, terrorism, and failing states present threats that cannot be managed without the capacity to deploy preventive force and engage in humanitarian intervention. The right to use force in these cases is not merely the best defense, as Sofaer rightly argues; it will often be the only defense.

Today, these uses of force are technically illegal, and the United States is left with little choice but to ignore the law. But doing so delegitimizes international law, thereby weakening support for U.S. actions and the United States itself. It would be much better to change bad rules for good ones and insist that courts -- and governments -- stick to the letter of the law.

Former Foreign Policy Counsel, U.S. Senate Republican Policy Committee