Defense Secretary William Cohen yesterday said the threat posed by asymmetric attacks upon areas of U.S. weakness will present a "major challenge" for years to come because of the United States' supremacy in nearly every aspect of conventional military power. The threat, Cohen said, was demonstrated by the recent attack upon the Navy destroyer Cole -- what he called an "indirect but highly effective" method adversaries may favor in the future. Similarly, he said at luncheon at the National Press...