"In this century, we learned through harsh experience that the only answer to aggression and illegal behavior is firmness," Mr. Clinton said while he still occupied the White House. "If we fail to respond today, Saddam, and all those who would follow in his footsteps, will be emboldened tomorrow by the knowledge that they can act with impunity, even in the face of a clear message from the United Nations Security Council." Yet Mr. Clinton did fail to respond. Saddam Hussein had four years to strengthen his arsenal, even as the sanctions effectively collapsed. According to Mr. Blix and...