WASHINGTON - The U.S. arsenal of nuclear weapons is declining in power and purpose while the military's competence in handling the world's most dangerous arms has eroded. At the same time, international efforts to contain the spread of such weapons look ineffective. Defense Secretary Robert M. Gates, for one, wants the next president to think about what nuclear middle age and decline mean for national security. Gates joins a growing debate about the reliability and future credibility of the American arsenal with his first extensive speech tomorrow on nuclear arms. The debate is attracting increasing attention inside the Pentagon even...