When President-elect Donald Trump officially becomes the president of the United States in January, he will take complete control of America’s nuclear arsenal. Should he decide to start a nuclear war, there are no legal safeguards to stop him. Instead, a much less tangible web of norms, taboos, and fears has reined in US presidents since World War II. But as North Korea escalates its nuclear weapons tests and the president-elect of the United States openly contemplates using nukes, experts worry that this fragile web could start to tear.