Confronted with mounting evidence that Iraq did not possess weapons of mass destruction at the time of last year's war, U.S. President George W. Bush and British Prime Minister Tony Blair last month decided to launch an independent inquiry into the quality of intelligence they used to justify the war. This is no small concern to Prime Minister Junichiro Koizumi, who supported the invasion and is now sending a large contingent of ground troops to postwar Iraq.

The investigation, it must be hoped, will clear up all relevant questions. How was intelligence gathered and analyzed? How was it used? More specifically, was it exaggerated, or manipulated, to build the case for regime change in Baghdad? If the war was started on the basis of false intelligence, as it now seems increasingly likely, then the legitimacy of the war -- and the credibility of President Bush's doctrine of a "preemptive attack" -- will be thrown into serious doubt.

Both Mr. Bush and Mr. Blair -- as well as Mr. Koizumi and other national leaders who backed them -- all believed, or seemed to believe, that former Iraqi President Saddam Hussein's regime was hiding those banned weapons somewhere in the months leading up to the war. The chief justification they provided for the military action was that those deadly arsenals, somehow concealed entirely from weapons inspectors, posed an immediate threat to regional and global security. That rationale now seems out of kilter with reality.