Some thoughts on a climbdown for the ages. The reaction was widespread relief in America and the world. Americans want their country to be the world’s growth engine but not, as a former Reagan administration official put it, through policies “that risk the collapse of the global financial system.” Donald Trump scared people he hadn’t scared before. He didn’t use to scare his policy allies—small-business people, workers, retirees. He did this week. Fear dampens reflexive support. Politicians need reflexive support from the bottom of their base as a platform from which to move. The president weakened his position. It is...