Why we're there: we went into Iraq, and persist there now, for sound reasons.

THE Bush administration has remained largely on the defensive in the escalating war of words over the merits of its decision to invade Iraq in 2003. In contesting the Democrats' key anti-war allegation--that the president "lied" the country into Iraq by misrepresenting the available intelligence--the White House has concentrated on the indisputable fact that everyone, Republicans and Democrats, Bush-administration officials and their Clinton-administration predecessors, the U.S. and dozens of foreign countries, believed that Saddam Hussein maintained stockpiles of chemical and biological weapons, at the least, and probably had an active nuclear program as well. There are, however, a number of other, equally compelling points that can and should be emphasized in defending the administration's Iraq policy.

THE LAW

First and foremost, it should be made clear that the legal case for war against Saddam's regime--a subject of continuing debate in Europe, the U.N., and the international-law professoriate--has not been undercut in any way, and certainly not by the failure to find WMD stockpiles in Iraq. This is true regardless of whether the war's legality is based on: the inherent right of the United States and its coalition allies to defend themselves against threats to their security; U.N. Security Council Resolution 678, which authorized the use of force against Iraq in 1991 both to expel Iraqi forces from Kuwait and to restore peace and security in the region, and which has never been withdrawn; Security Council Resolution 1441, passed in the fall of 2002 and finding Iraq to be in "material breach" of its obligations under various preceding resolutions; or some combination of the above. None of these justifications depended on the actual existence in Iraq of WMD stockpiles, and the use of military force was not, therefore, "illegal."

In this connection, it should be emphasized that at no time was it the responsibility of the U.N. inspection teams, or the United States and its allies, to establish that Saddam Hussein retained a WMD capability. The onus of proving that he had fully disarmed was always on Saddam. This was the price of an armistice, and of keeping his odious regime in power following Iraq's defeat in the first Gulf War. From a legal point of view, his failure to meet this burden fully justified military action.

LIVING WITH SADDAM

It is perhaps more pertinent to the current debate, however, that the threat assessment upon which the Bush administration acted was fundamentally sound. The only mistake in its calculus, made by the CIA and numerous foreign intelligence services, was positing that Saddam possessed stockpiles of chemical and biological weapons--as well as a concealed nuclear-weapons program--after 1991. It was, however, an honest mistake. The claim that Bush lied about Saddam's WMD is itself a lie. There is no doubt that the administration sincerely believed that Saddam retained a substantial WMD arsenal.

Indeed, the U.S. viewed the WMD threat as so serious that all of its pre-war planning, including the timing of the attack and the actual combat operations, was conducted in the full expectation that Saddam would use at least chemical weapons against U.S. troops. U.S. troops carried gas masks and chemical suits into battle. Moreover, it would have made no sense for the administration to rely so heavily on the WMD threat to publicly justify military action if it knew that no WMD would be found once Saddam was toppled.

In any case, Saddam's supposed WMD stockpiles were only one aspect of the threat calculus. The other critical elements encompassed the undisputed facts that Saddam had proven himself to be an aggressive and unpredictable actor in a highly important and vulnerable area of the world; that he had had WMD capabilities (including a mature nuclear-weapons program) in the past; that he had already deployed and used WMD against both Iranians and Iraq's own citizens; that he had sheltered known terrorists and aided active terrorist organizations; and that he had never fully cooperated with the U.N. inspection teams. In other words, Saddam Hussein was a dangerous man behaving as if he had something to hide.

Significantly, none of the major opponents of military action in Iraq--including and especially France and Germany--ever claimed that Saddam had, in fact, met his obligations and was no longer a threat. Like those members of Congress who voted against the use of force in the fall of 2002, their alternative was to continue a policy of containment. They did not, of course, offer to take up the burdens and risks of this policy: It is the United States and Britain that would have continued indefinitely to enforce the no-fly zones and guarantee the region's security from Saddam.

Even more to the point, the U.N. sanctions regime was crumbling. Indeed, by the end of Bill Clinton's second term, Britain and the United States were the only permanent members of the Security Council who supported continuing (let alone tightening) the sanctions against Saddam Hussein's government. Partly for commercial reasons, partly driven by reflexive anti-Americanism, partly because of Saddam's Oil-for-Food bribes, and partly in simple diplomatic exhaustion, France, Russia, and China were eager to grant the regime in Baghdad a clean bill of health. And in any case, even if an all-out U.S.-led diplomatic effort could have resuscitated the sanctions policy for a time, it was fundamentally unsustainable for the long haul. Even the most targeted sanctions would have hurt individual Iraqis more than Saddam, whose allies had made adroit use of Iraqi suffering, some real and some exaggerated, to advance their agenda.

Moreover, once the sanctions regime finally collapsed, other efforts to keep Saddam "in the box" would probably also have failed. The legality of the Anglo-American-enforced no-fly zones would certainly have been challenged. Indeed, it is difficult to imagine that the Turkish government would have allowed America to conduct continued combat missions against Iraq from its territory once Saddam was no longer the subject of international sanctions. At the same time, the specter of Saddam's brutally reestablishing his control over Iraq's Kurds and Shiites in the early 1990s, and his survival after ten years of war and sanctions, had buttressed his prestige in the Arab world.

In this context, it is doubtful that Iraq's neighbors would have been able to sustain a long-term containment strategy similar to NATO's policy toward the Soviet Union during the Cold War. Had Saddam regained his international legitimacy, along with the practical (if not formal) end of sanctions, other states in the region would likely have tried to reconcile themselves with his regime, U.S. efforts to oust him having failed. The fear of Saddam felt by key Persian Gulf leaders, and their resulting anxiety to participate in any anti-Saddam ventures, was vividly manifested by their frantic efforts to obtain unambiguous assurances in 2002 and 2003 that the United States would finally effect regime change in Baghdad. These efforts--in the person of Prince Bandar, Saudi Arabia's ambassador to the U.S., who demanded commitments directly from President Bush--are vividly described in Bob Woodward's Plan of Attack.

Amidst this cascade of negative foreign-policy consequences of Saddam's revival, the military threat from Iraq also would have increased. Although Saddam evidently chose not to reconstitute his WMD stockpiles while the sanctions were in place, the notion that he would have forgone these weapons once sanctions were lifted is fanciful. Saddam Hussein had spent years and billions of dollars developing chemical, biological, and nuclear programs for a reason; and, like Adolf Hitler, he never disguised his ultimate ambitions. Saddam saw himself as a new Saladin, a man destined to become the Arab world's dominant if not actual leader. Both men were, in fact, born in the same town (Tikrit), although Saladin was of Kurdish and not Arab extraction. WMD played a major symbolic role in advancing Saddam's grandiose ambitions, and over the long run that symbolic role would likely have become a literal one.

The fact that Saddam appears to have practiced an elaborate deception reminiscent of Nikita Khrushchev's famous missile bluff of the 1950s, proclaiming that he was fully disarmed but acting as if he retained his WMD stockpiles, simply underscores the extent to which he saw WMD as a psychological cornerstone of Iraq's grand strategy. With hundreds of billions of dollars of oil revenues at his disposal, and freed from the need to play a cat-and-mouse game with the U.N. inspectors, he could easily have re-created these stockpiles and reconstituted his nuclear program.

Finally, even without WMD, the wealth, population, and strategic location of Iraq would have allowed Saddam to continue posing a grave threat to the stability of the Persian Gulf region. While this point is all but forgotten in today's debates, it was a key aspect of the U.N. resolutions on Iraq. These effectively required Iraq not just to evacuate Kuwait and disarm, but also to cease being a "threat to peace" in the region. How that threat could have been eliminated while Saddam remained in power is not apparent.

AND THEN CAME SEPTEMBER 11

The threat assessment that led to the 2003 invasion of Iraq was inevitably shaped by al-Qaeda's attacks on the United States in 2001. Unfortunately, this aspect of the debate has focused almost entirely on whether Saddam Hussein was actually involved in planning or facilitating those attacks. It now seems clear that Iraq was not directly involved, but the Bush administration never claimed it was. What the administration did point out was that Saddam Hussein sponsored terrorism. His Baathist regime had directly supported global terrorist activities and provided sanctuary for individual terrorists, including Abu Abbas, the man responsible for the 1985 attack on the Achille Lauro and the murder of American Leon Klinghoffer, and Abu Nidal, the mastermind of attacks at El Al ticket counters in Europe that left 18 people dead. And, as described by The Weekly Standard's Stephen F. Hayes, captured Iraqi intelligence archives describe numerous contacts between Iraqi officials and al-Qaeda operatives.

Moreover, the notion that radical Islamists and secular Arab fascists would not make common cause against the United States simply because they have different ideologies is highly dubious. To begin with, Saddam had in recent years tried to win the support of Islamists with such gestures as the addition of a Koranic verse to the Iraqi flag. The more fundamental point is that, whatever their differences, Baathists and Islamists share the goal of driving American forces and influence from the Middle East. We have seen Middle Eastern secular and religious groups cooperate routinely in Iraq, Afghanistan, and Palestine. More generally, history is replete with examples of ideologically diverse states and groups allied against a common enemy. Nazi Germany and Imperial Japan had ideologies that involved notions of their own racial superiority and would, therefore, have been incompatible with each other over the long term. Yet they cooperated with each other during the Second World War; and few would argue today that President Roosevelt was foolhardy to view them as posing a joint threat to America's security, or that he was wrong to meet that threat in a decisive manner.

Far more important, however, is the fact that September 11 fundamentally shifted our strategic calculus of what constitutes a tolerable threat level. The attacks on the World Trade Center, the Pentagon, and potentially the U.S. Capitol or White House dramatized the extent of American vulnerability and the degree to which America's will had been underestimated by its enemies. Osama bin Laden considered the United States to be a "weak horse" doubtless in part because Saddam had survived a decade despite what he must have taken to be America's best efforts at stopping him. In any case, once al-Qaeda showed that entities in the Middle East could successfully attack the American homeland, the danger of allowing Saddam to endure was substantially magnified. Regime change in Baghdad had been an avowed American policy since the Clinton administration, but its execution gained urgency after September 11, which dramatically altered our geopolitical paradigm and provided a powerful justification for acting immediately--especially since, by 2003, it was clear that Saddam could not be removed from power by either diplomatic means or covert action (all of the CIA's efforts to facilitate a coup in Baghdad having failed).

WINNING THE DEBATE

Of late, the administration has become more effective in arguing that the United States cannot simply withdraw from Iraq--a course of action urged by a growing chorus of Democrats and even some Republicans. Such a withdrawal would encourage and embolden the Islamists, just as the American withdrawals from Somalia in 1994 and Lebanon in 1984 informed bin Laden's calculations about U.S. staying power in the Middle East. In addition, there is every reason to believe that a precipitous American pullout would lead to the Talibanization of Iraq, which would serve as an even more congenial host for al-Qaeda and its allies than was Afghanistan before its liberation. Abandoning our Iraqi mission would also validate, in a practical if not a legal sense, the terrorist tactics used by the "insurgents." If the United States cannot face and effectively counter these tactics, it will indeed become a Gulliver bound by the world's most vicious Lilliputians.

The cost in American blood and treasure in Iraq has been great--although far less than in previous wars, including Vietnam. The administration in Washington and military commanders in Iraq have obviously made mistakes, and have occasionally been bested by the enemy. This, however, is to be expected in any war. War cannot be choreographed. Battlefield intelligence is always imperfect, uncertainties and unforeseen events foil the best-laid plans, and the enemy adapts and learns how to offset one's strengths and exploit one's weaknesses. The victor is not the party that makes no mistakes, but the one that learns from its mistakes better and quicker. Both American forces in Iraq and the Bush administration have learned much in the past two years, and U.S. military operations in Iraq have, on the whole, been remarkably flexible and successful.

But even if the Iraq war had been fundamentally mishandled so far, it would not follow that withdrawing is the right amelioration. Recognizing this, the war's critics have begun alleging that the U.S. military presence in Iraq is making the insurgency more powerful and creating new jihadists worldwide. But even if the U.S. military presence has antagonized some Iraqis, many others--especially Shiites and Kurds, the past victims of Baathist violence--want U.S. troops to remain until the insurgency has been defeated. That insurgency is fueled both by foreign fighters and by the desire of some Sunnis to prevent the creation of a genuinely pluralistic society in which Shiites and Kurds enjoy access to political and economic power. Even if U.S. forces evacuated and the foreign fighters followed--not necessarily a desirable outcome from America's perspective--these unreconstructed Baathists would remain. More broadly, withdrawal would be taken as an acknowledgment that we cannot engage terrorists or their sponsors on their own soil, and set a precedent for isolationism and retreat.

Emboldened by opinion polls showing eroding support for the Iraq mission, the Bush administration's political opponents have portrayed our choice as being immediate withdrawal or phased but prompt disengagement. Victory is no longer discussed or, if truth be told, desired.

A defeat in Iraq means a failed Bush presidency--and that has become the critics' overarching goal, regardless of costs to American interests. Those costs would be high indeed. They would not be limited to a renewed "Vietnam Syndrome" and decline in American prestige. Insurgency would surely be used by future enemies of the United States, the assumption being that America cannot win a protracted engagement on foreign territory--be it with a formidable adversary like North Korea, a second-class foe like Syria, or even a third-rate regional power like Venezuela.

Failing to complete what has been started in Iraq would, in other words, light the way for every one of America's future enemies, and would severely complicate American diplomacy and defense interests well beyond the Middle East. The perception of America's military prowess is critical to its ability to maintain friendships and alliances around the world, including with such countries as Japan and India, which look with alarm upon China's growing military might.

The administration should accept that it is now fighting a two-front war--one in Iraq and one in Washington. Of the two, the Washington-centered war of words may be the decisive one; if the president wins the battle of public opinion, there is little doubt that U.S. forces can win the war on the ground in Iraq. Fortunately, recent speeches by both the president and the vice president suggest that the administration has accepted this stark reality, and that it is beginning to fight back.

Messrs. Rivkin and Casey are partners in the Washington, D.C., offices of Baker & Hostetler LLP, and served in the Justice Department under Presidents Reagan and George H. W. Bush. The views here expressed are their own.