Former Vice President Joe Biden frames his run for president as a “battle for the soul of this nation.” Three times in his campaign announcement, he used the phrase “who we are.”

Former President Barack Obama made it popular in Democratic politics to talk about “who we are” and to castigate what he wanted people to regard as un-American beliefs with the phrase “that’s not who we are.” Distinguishing between American and un-American beliefs was, a long time before the Obama era, easy, for the nation was indeed bound together by many shared assumptions and values. But Obama himself, among others, did much to unpick those unifying ties, and these days, as the culture wars heighten, it’s getting harder to say with any assurance what is and what isn’t American.