U.S. National Security Adviser John Bolton says he's trying to stay optimistic and realistic at the same time following North Korea's summit cancellation threat.<br /> Speaking to Fox News Radio on Wednesday,... Bolton said the U.S. will do everything it can to have a successful meeting,... but will not back away from its objective,... which is a complete, verifiable and irreversible denuclearization of North Korea. <br />Bolton added he has spoken to his South Korean counterpart, Chung Eui-yong on the possible reasons behind North Korea's sudden about turn. <br />
