Donald Trump and Jeff Bezos inhabit very different worlds. The president is a staunch bricks-and-mortar man who made his fortune building towers and dealing with blue-collar workers. The founder of the world’s largest store, by contrast, is a space enthusiast who experiments with robots and operates much of the cloud where the new economy’s data lives. Trump’s decision in recent days to zero in on Bezos and Amazon.com as his latest Twitter targets has highlighted a severe fracture in American society, a divide between concrete and steel and zeros and ones, a split that is as much philosophical as it is economic, as much about the fraying of communities as it is about the shape of commerce. Four times over the past week, the president has criticized Bezos for running a company that he says fails to pay its share of taxes, for taking undue advantage of the struggling U.S.