North Korea cheered this month when a man with a knife and a history of violent behavior slashed the face of Mark Lippert, the U.S. ambassador to South Korea. The attack in Seoul was "a knife shower of justice," North Korea said, praising it as "deserved punishment for warmonger United States." If that sounds mean-spirited, consider this: For years, North Korea has taught schoolchildren to bayonet effigies of U.S. soldiers. Under its young dictator, Kim Jong Un, the government has suggested it