A day after North Korea moved a missile to the east coast, South Korea is moving two missile-defense warships to track a potential launch. “If the North fires off a missile, we will trace its trajectory,” an official told the Yonhap news agency. The missile moved yesterday is believed to have a range long enough to reach Guam, which North Korea said would be a target. Yesterday the U.S. said it would deploy a missile-defense system there in response to the threats. In addition to moving missiles, North Korea has shut down an industrial zone shared with the South, promised to restart a mothballed nuclear reactor, and threatened nuclear strikes against South Korea and the U.S.