By addressing President Trump in a personal statement on Friday, the nation’s leader, Kim Jong-un, has pushed his government’s brinkmanship to a new, potentially more perilous level. In a statement written in the first person, published on the front pages of state newspapers and read on national television, Kim Jong-un called Trump a “mentally deranged U.S. dotard” who had “denied the existence of and insulted me and my country in front of the eyes of the world.” Kim vowed to take the “highest level of hard-line countermeasure in history.” His decision to respond personally to Trump’s speech to the United Nations General Assembly and pledge reprisals escalated the standoff over the North’s nuclear program in a way that neither he nor his predecessors had done before.