The comments Sunday by weapons inspector David Kay were the most succinct argument to date against pre-emptive war. Speaking of his inability to find weapons of mass destruction in Iraq he said his predictions that he would find weapons were not “coming back to haunt me in the sense that I am embarrassed. They are coming back to haunt me in the sense of ‘Why could we all be so wrong.'”

Not all, but many people, including those in the Clinton administration, thought Iraq had made significant advances with these weapons. Now it looks likely that the progress was only on paper and much more one of intention than fact. The White House at first maintained its conviction that WMD would be found. But the fact that both the president and the secretary of state are now referring to “weapons-of-mass-destruction-related program activities,” the very vagueness of which renders the phrase meaningless, is a sign that they understand their earlier assumptions may have been wrong.

Before the war, British Prime Minister Tony Blair urged that U.N. inspectors be given more time to inspect Iraq for weapons. In supporting the case for war he seemed nevertheless to understand that the standard of evidence for showing a clear danger was high. The Bush administration believed that it had sufficient evidence through intelligence reports. Why it believed this has in the press piled conspiracy theories on top of conjecture without conclusion. Whatever the administration’s reasoning, it is fairly certain that, even if some level of WMD is eventually found, the intelligence reports overstated their amounts and the potential threat to the United States.

Since the first phase of the war ended, a primary justification for fighting it has been that Saddam Hussein was a tyrant, a man who tortured his own people and continually went to war with others. Mass graves show the extent of his evil. The administration did not spend a lot of time publicly with this argument before the war, and the reason was clear enough: the cause of mass murder as grounds for a U.S. invasion would have American troops sent all over the world. The argument has greater attraction for the administration now because Saddam Hussein was successfully chased from his palace and plucked from his spider hole and because it distracts from the weapons reasoning.

But Mr. Kay’s point is the important one: Information can be wrong and further wrongly interpreted, with world-changing consequences. If the administration is to hold onto its policy of pre-emptive war, it should recognize the friend it has in Mr. Kay and publicly review where it erred in judgment and what standards of evidence it would do better to use in the future.