Some in Congress and abroad, of course, will not be persuaded to support action against Iraq, no matter how much evidence is laid out about the threat posed by Saddam Hussein; the administration cannot allow itself to be paralyzed by unreasonable demands for smoking guns. In fact, there is abundant evidence already in the public record that Saddam Hussein retains stockpiles of chemical and biological weapons and delivery vehicles in violation of U.N. resolutions, that he seeks to acquire nuclear arms, and that he is willing to use these weapons to realize his long-standing ambition to establish dominion over the Middle East and its oil supplies. Those who insist on still more conclusive proof, especially of an Iraqi nuclear program, are essentially arguing that it would be better to take action only after Saddam Hussein conducts a nuclear test or a terrorist group uses a chemical or biological weapon acquired from him. In the post-9/11 world, such a strategy is self-defeating and dangerous.

Yet to succeed, any action against Iraq will require broad and sustained support from Americans and foreign allies. That would certainly be true of any effort to reintroduce a U.N. inspection regime, which even proponents describe as unlikely to succeed; but it would be even more true of the intervention many senior administration officials have in mind: a full-scale invasion of Iraq and the replacement of Saddam Hussein's regime by a democratic government. Such an enterprise would likely cost thousands of Iraqi or American casualties, tens of billions of dollars and years of U.S. effort to occupy and reconstruct a large and complex country; it would dwarf the Balkan interventions that Mr. Bush once portrayed as stretching the U.S. military too thin. Americans, and Congress, are more likely to accept such costs if they are forthrightly estimated and weighed before action is taken. Administration officials have so far ducked the question; it is vital that Congress press for answers in upcoming hearings.

Similarly, while the United States may be able to win a war against Iraq on its own, it is difficult to imagine how any project to remake Iraq after Saddam Hussein could succeed without major allied contributions of troops, funds and political goodwill. One key to winning such support is a plan for Iraq's future, including a commitment to the kind of forceful nation-building that the Bush administration has criticized in the Balkans and evaded in Afghanistan; the absence of any such plan is one of the principal worries of European and Arab leaders. Still more important would be a demonstration of U.S. willingness to build an international coalition, even if that meant accepting such dilatory steps as offering a last chance to inspections, or enduring a few rounds of negotiations in the Security Council. In the end such process, even if fruitless, would probably bring most of the necessary allies on board; by contrast, offering the world a precooked and nonnegotiable buildup to war could well doom an Iraq mission before it begins.