U.S. Defense Secretary Jim Mattis turned up the heat on North Korea and its main benefactor, China, on Saturday, calling the North Koreans a "clear and present danger" and chastising the Chinese for coercive behavior in the South China Sea. His sharp words for both countries suggest he believes China will, out of self-interest, exert leverage on North Korea to halt its nuclear and missile programs even as Washington pushes Beijing to change course in the South China Sea.