If there was a single moment – a stroke of a quill, you might say – when the idea of America was hatched, it was this: While drafting the Declaration of Independence, in the section where he lists grievances against the distant British monarch King George III, Thomas Jefferson made a revision. He scratched out the word “subjects” and recast his compatriots as “citizens.”

The word is central to American thought. But it is also a conundrum. As the historian William Novak observed, “The word citizen or citizens is found ten times at least in the Constitution of the United States, and no definition of it is given anywhere.” Another historian, Jill Lepore, devoted a lengthy chapter to the question in her book “These Truths,” chronicling how Congress and the courts jousted toward a legal definition in the decades after the Civil War that remains contested today.

Yet, when disentangled from political expediency, lawyerly syllogism, and economic interest, which have beclouded Jefferson’s declaration of equality…