A year has passed since Donald Trump astounded the world by winning the 2016 presidential election. It has been one of the most fraught 12 months in American history. It is a cliché to say that the United States is a deeply divided society, but those divisions have been made more intractable by the way Mr Trump has exercised the presidency. Instead of bringing the nation together, as presidents of left and right have done for generations, he has increased its fragmentation.