This is, in a very real sense, the moment of truth. A top priority for the invading forces is to establish on the ground, in Iraq, the existence of weapons of mass destruction. This, President Bush held, was what left him no choice but to intervene without further delay and without UN authorization.
Mobile laboratories and teams of specialized experts have been deployed in the hope that weapons caches will be uncovered in the first days of the invasion - before they can be diverted to other countries or into the hands of terrorists.
Mr. Bush remains convinced there are chemical and biological weapons stores in Iraq. The nuclear weapons picture is more clouded. Atomic weapons inspector Mohamed ElBaradei has said, "There is no indication of resumed nuclear activities." He has dismissed US intelligence about uranium purchases in Africa as based on forged documents.
Still, on television Sunday, Vice President Dick Cheney insisted, "We believe [Saddam Hussein] has, in fact, reconstituted nuclear weapons." President Bush, on television Monday evening, was more cautious. He spoke of the danger of chemical and biological, "or, one day, nuclear weapons."
Any discovery by the invading forces of banned weapons that UN inspectors missed, or had been barred from seeing, would, of course, be a triumph for Bush. It would also be a world-class embarrassment for the French, the Germans, and others who've opposed use of force.
Of course, failure to find banned weapons doesn't prove anything. Presumably, Hussein could have sent them abroad or destroyed them. But it would be a great thing for international relations if this moment of truth produced some ... truth.
The resort to arms is not only "the end of a diplomatic process," as Bush said. It marks the erosion of the concept of collective security that has underpinned US policy from Wilson to Clinton.
The effort to get a warmaking license from the UN Security Council, which the Bush administration had said it didn't really need, was defeated by citizen resistance in some of the countries where citizens can exercise influence.
Britain's Tony Blair pleaded in vain for a resolution that might help get him out of hot water with his constituents. Mexico and Chile need many forms of American help, but they discovered that they need the consent of their citizens more. France, where you can make a career of America-bashing, is a story of its own. So is Russia, which doesn't need voter pressure in order for President Putin to make trouble for Bush.
Bush proclaims himself devoted to the spread of democracy, but he is not always happy with the results.
To a group of veterans assembled at the White House last November, he said, "We don't seek an empire. Our nation is committed to freedom for ourselves and for others."
Yes, but the current Newsweek magazine carries a lengthy article entitled "The Arrogant Empire," saying that never will America have waged a war in such isolation as the war with Iraq.
• Daniel Schorr is a senior news analyst at National Public Radio.