Trump recasts America not as an abstract creed but as a civilization rooted in a distinct people—arguing that change the people, and you change the nation itself. Here are two quotations, one from Donald Trump this week and one from Thomas Jefferson. I won’t tell you which is which. Here’s the first: “For nearly two centuries before the revolution, this land [America] was settled and forged by men and women who bore in their souls the blood and noble spirit of the British. Here on a wild and untamed continent, they set loose the ancient English love of liberty and...