It is among the odder ironies of modern political life that the Fourth of July, a holiday set aside to celebrate American exceptionalism, has become an occasion to proclaim multicultural pieties. For a vivid demonstration of this tendency, look no further than the habit of our high-minded commentators to lecture every Independence Day that “we are a nation of immigrants.” In in its most extreme incarnation, this claim holds not only that America has been “a nation of immigrants from its very inception” – an observation equal parts true and misleading – but that any reflection on the American character...