Alex Edelman/picture-alliance/dpa/AP Images Supporters hold campaign signs during a Make American Great Rally at Atlantic Aviation in Moon Township, Pennsylvania W hen Trump and his followers refer to “America,” what do they mean? Some see a country of white English-speaking Christians. Others want a land inhabited by self-seeking individuals free to accumulate as much money and power as possible, who pay taxes only to protect their assets from criminals and foreign aggressors. Others think mainly about flags, national anthems, pledges of allegiance, military parades, and secure borders. Trump encourages a combination of all three—tribalism, libertarianism, and loyalty. But the core of our national identity has not been any of this. It has been found in the ideals we share—political equality, equal opportunity, freedom of speech and of the press, a dedication to open inquiry and truth, and to democracy and the rule of law. We are not a race. We are not a creed. We are a conviction –...