Since the US first emerged as a world power in the late 19th century, there has been a tacit assumption around the world that the president of the United States would always be competent and rational. Whether other governments and peoples loved him or reviled him, they always assumed that the president would not be a fool or a lunatic. It was conventional wisdom that the American ruling class would not allow such a person to reach the office. That assumption has been shattered now. We have entered a new and very dark era.