The authority of Missouri v. Holland is in no way impaired by developments of the last decade. While Justice Holmes rejected the view that "invisible radiation" from the Tenth Amendment could restrict the treaty power, his approach accepts that a treaty cannot violate "prohibitory words" in the Constitution. Some prohibitory words explicitly protect the interests of the states as against the national government. For example, the framers clearly meant the prohibition in Article I, section 9 on export taxes to bar one form of potential federal taxation that the Southern states found worrisome. In the face of this specific prohibition, which was motivated by federalism concerns, a treaty to impose an export tax would presumably be as unconstitutional as the legislative measures that the Supreme Court has already invalidated under the clause. There is thus enough protection for the interests of the states qua states in the prohibitory words analysis, as well as in the practical and political safeguards of the processes for making international agreements.
International Law | Law
Lori F. Damrosch,
Treaties and International Regulation,
Am. Soc'y Int'l L. Proc.
Available at: https://scholarship.law.columbia.edu/faculty_scholarship/4098