In the summer of 2017, North Korean leader Kim Jong Un launched an intercontinental ballistic missile (ICBM) that landed about 200 miles off the coast of Japan. He also threatened the United States with an ICBM strike. Sullivan said, "In fact, for over a year, the experts have been saying it’s not a matter of if, but when North Korea will develop an [ICBM] that could hit not only Alaska and Hawaii, but the entire continental United States.” Sullivan supports improving the United States' missile defense system (MDS). The U.S. Department of Defense, as of 2017, was conducting a missile defense review targeted at strengthening the nation’s defensive abilities, studying whether to place missile interceptor sites on the east coast or in the Midwest, and recommending funding priorities. The report was due to Congress at the end of 2018.