Ilya Somin has written that the “detailed list of congressional powers in Article I of the Constitution does not include any general power to restrict migration.” Specifically, he contends, this authority cannot be derived from the Naturalization Clause, the Commerce Clause, the Migration or Importation Clause, or any sort of inherent aspect of sovereignty (as John Eastman counters).

Robert Natelson writes in The Hill of another provision in Article I that supports federal immigration laws: the Power to “define and punish . . . Offenses against the Law of Nations.” Natelson, and his co-author, Dave Kopel first wrote about this clause nearly seven years ago in a response to Jack Balkin’s claim that immigration laws can be supported by the Commerce power. They explained in the Michigan Law Review Online:

One example was governance over the immigration and emigration of free persons, which Balkin several times erroneously attributes exclusively to the commerce power, but which the Constitution granted to Congress as part of its authority to “define and punish . . . Offenses against the Law of Nations.”16

16 See EMER DE VATTEL, THE LAW OF NATIONS 220–27 (Knud Haakonssen, ed. 2008) (originally published 1758) (discussing emigration and immigration as a division of international law). Vattel’s work was the most important book on international law during the Founding Era.

Natelson elaborates at length in The Hill:

“The law of nations” was the usual 18th-century term for international law. It included standards of conduct among nations. But it also encompassed some rules within national boundaries. A power to “define and punish” an “offense against the law of nations” included protecting foreign ambassadors against interference, protecting safe-conduct passes — and restricting immigration.

Why have so many writers — including some constitutional law professors — missed this? One reason is that 18th-century legal terms and categories were different from those we use today. For example, a modern law book might feature a heading for “immigration law.” But in William Blackstone’s “Commentaries,” the English book that served as America’s most popular legal treatise, there was no such heading.

Instead, Blackstone addressed the topic in his chapter on the British king’s prerogative powers. When discussing safe-conduct passes, Blackstone observed that without them “by the law of nations no member of one society has a right to intrude into another … [I]t is left in the power of all states, to take such measures about the admission of strangers, as they deem convenient.”

Blackstone relied partly on the writings of Samuel Von Puffendorf, a German international law scholar. Puffendorf’s writings were familiar to Americans. Even more popular were the writings of the Swiss lawyer, Emer de Vattel. His famous book on international law did not have a topic entitled “immigration.” But it did discuss both immigration and emigration as part of the law of nations. For example, Vattel wrote that in “Switzerland and the neighboring countries … the law of nations … did not permit a state to receive the subjects of another state into the number of its citizens.”

This should teach us two civic lessons. First, the Constitution did grant the federal government authority over immigration. Second, to understand the Constitution you have to do more than read the document. Because it was written mostly by lawyers for an 18th-century public well educated in legal matters, to fully understand the Constitution we have to know some fundamentals of 18th-century law.

Natelson makes a compelling case that I have not seen addressed elsewhere.