Bond had argued that the power to “make treaties” was limited either by the Tenth Amendment or the overall doctrine of federalism. Conservative groups were eager for the Court to create new rules about what matters treaties could cover as a way to stymie contemporary treaties that concern things like environmental protection and human rights.

Making treaties is a sovereign power; an independent nation must have it. The framers of the Constitution gave that power to the president and two-thirds of the Senate. Article VI § 2 makes “treaties ... which shall be made under the authority of the United States” part of “the supreme law of the land,” explicitly trumping “any thing in the constitution or laws of any state to the contrary notwithstanding.” It nowhere hints that federal courts must approve these treaties, nor that states can block them.

There’s an established rule of construction called the avoidance doctrine: If there are two ways of reading a statute, and one way would cause a serious constitutional problem, a court should read it the other way. That’s what the majority in Bond did. It concluded that Congress did not intend its statute to extend to local disputes like the Bond-Hayes feud.

This is a long-standing principle. When a federal statute punishes a crime, the Court will read it narrowly to avoid trenching on states’ powers. It Congress wants to reach purely local matters, it must spell its intent out clearly.

One prominent treatise endorses that rule and cites a “straightforward case.” A federal statute made it a crime to “knowingly mak[e] any false statement or report” to get money from a bank. Were bad checks “false statements”? The authors approve the Court’s 7-2 decision that “Congress should have spoken in language that is clear and definite” if it had really wanted to “put the federal government in the business of policing bad checks.”

Remarkably, one of the co-authors of that very treatise, Antonin Scalia, disagreed furiously Monday. In a concurrence, Scalia was eager to chew a huge hole in the Treaty Power. His proposed rule: The federal government has the power to “make treaties”—but has no power, by legislation or otherwise, to “implement treaties already made.” Once a treaty is “made,” the federal government could recommend to the states various measures to enforce it, but that is it.

Thomas and Alito had radical new rules of their own to suggest. (Both joined part of Scalia’s opinion.) Thomas would have used this case to hold that “[e]ven if a treaty may reach some local matters, it still must relate to intercourse with other nations.” Alito suggested that “the treaty power is limited to agreements that address matters of legitimate international concern.”

Scalia’s rule would in effect reduce the federal government into an ineffectual scold. Thomas’ rule—or Alito’s—would make federal courts the overseers of foreign relations. Under either, the government could sign any treaty that struck five justices as addressing “legitimate” international concerns.