State sovereignty is the fundamental building block of the international legal system. International Law, much like the US Constitution, is at once an expression of, and self-imposed limitation upon, sovereignty. At the same time, international law is much less of a limitation on US sovereignty than is the US Constitution, and rightly so.
Today’s international legal system is a strongly positivist, consent-based system. In general, states are not bound by any rules of international law that they have not themselves created or otherwise consented to. While states have chosen to greatly expand the scope and substance of international law, most of its rules remain in the form of broadly formulated obligations that leave the manner of their implementation in the broad discretion of states.
The US has been a proponent of the development of international law since the founding of the country, and this is reflected in its constitutional order. The Constitution of the United States was not created in a vacuum. It was well understood by the framers that they were drafting the Constitution against the backdrop of international law. They consciously chose to buy into the international legal system because it was clearly advantageous to do so. They wanted recognition as a sovereign equal, and all of the rights and protections that international law provided to states.
The international legal system of that time was a system largely oriented toward co-existence, and was one of relatively few rules. Since that time, there has been a dramatic expansion in international law, driven largely by the need for international cooperation in tackling the world’s ills and in harnessing its opportunities. The United States has played a central and powerful role in this evolution. Successive US governments have consented to be bound by literally thousands of treaties, and have supported the creation of dozens of international institutions. The US also frequently engages in treaty negotiations even in situations where it is clear that the US will not become a party to the treaty being negotiated. The robust engagement of the US in this process results from the recognition that international law and international institutions are useful in serving US interests.
No one would dispute the importance of federalism and the separation of powers in the US constitutional system. But these principles are not at odds with robust engagement in the international legal system or a disposition toward compliance with international legal obligations. The difference that has arisen seems to me to be one of locating the burden of inertia. It is my view that the default position of the US constitutional system is, and ought to be, a disposition in favor of compliance. For this reason, the doctrine of self-execution should be understood as a means of facilitating compliance.
The doctrine of self-execution
As noted above, international law generally does not dictate how international obligations are to be implemented within the domestic sphere. In the absence of a specific obligation in a treaty to alter some facet of a state’s internal legal framework, it is usually up to each state to determine how to give effect to its international obligations. That being the case, there is no established international legal standard governing how international law is to be received in the municipal sphere. As a result, there is a great variety among states in the degree of penetration of international law into the domestic legal system.
The US constitutional design, consistent with the attitudes of the framers toward international law, favors the reception of international law into its internal legal order. The U.S. Constitution declares that treaties made under the authority of the United States, together with the Constitution and federal law, “shall be the supreme Law of the Land.” The U.S. legal system appears equally amenable to customary international law. As the Supreme Court in The Paquete Habana famously proclaimed, “[i]nternational law is part of our law, and must be ascertained and administered by the courts of justice of appropriate jurisdiction, as often as questions of right depending upon it are duly presented for their determination.”
With regard to treaty law, U.S. courts have developed a doctrine of self-execution, whereby a treaty is to be regarded as “equivalent to an act of the legislature” when “it operates of itself without the aid of any legislative provision.” Such a self-executing treaty does not require any additional legislative act to render it applicable as part of U.S. law. However, “when either of the parties engages to perform a particular act, the treaty addresses itself to the political, not the judicial department; and the legislature must execute the contract before it can become a rule for the Court.”
This doctrine, which is a doctrine of US law and a further expression of US sovereignty, is based on the presumption that the US intends to comply in good faith with the international obligations it has voluntarily undertaken. Understood as a means of facilitating compliance with international law, it is consistent with the design of the Constitution and the intentions of the framers. For this reason, and in keeping with the jurisprudence of the Supreme Court that developed the doctrine, treaties should be presumed to be self-executing.
As noted above, this is simply a question of adopting a default position. In the event of a conflict between a rule of U.S. federal law and a rule of international law applicable as U.S. law, the later in time rule prevails. Thus, a later in time federal statute will override, within the framework of the U.S. legal system, a self-executing treaty provision. Thus, Congress can always effectively overrule a judicial finding of self-execution by enacting legislation.
The same is true for decisions of international courts, the jurisdiction of which is again consent-based. Where the US is subject to a binding judgment of an international court, as, for example, in the Avena case before the International Court of Justice (ICJ), the judgment should be regarded as applicable US law. If the US decides that it does not wish to implement that judgment within the framework of the US legal system, that option remains open, but it would require Congressional legislation. This would leave the default position of the US legal system as one of compliance, which is as it should be. Non-compliance should be exceptional, and affirmative steps should be required for the US to choose not to comply with an international obligation.
I therefore disagree with the approach of the US Supreme Court in the case of Medellin v. Texas, which held judicially unenforceable in US courts a judgment of the International Court of Justice. The Court essentially held that ICJ decisions are not enforceable within the US in the absence of enabling legislation. The fundamental problem with the Medellin judgment is that it leaves non-compliance with ICJ judgments as the default position. The default position should be compliance, and as such, judicial enforceability. If there are compelling reasons for non-compliance, the burden should be on the executive and the legislature to adopt measures to that end.
Mention also should be made here of the occasional practice of the Executive to append to instruments of ratification understandings that a treaty is or is not self-executing. These understandings should not be considered in determining whether a treaty is self-executing. The doctrine of self-execution is a judicial doctrine. It is up to the courts to determine on the basis of the text of each treaty whether it is amenable to direct application as US law. This falls within the power of the courts to determine and interpret the applicable law.
The power to interpret international law
The US President certainly has the power to interpret international law, just as he has the power to interpret any rule of applicable law. This power is a necessary incident to his role as Chief Executive. At the same, the President is of course not the exclusive interpreter of any law. This is a fortiori the case when it comes to international law, which is subject to interpretation not just by other branches of government and other federal, state, and local officials within the US, but also by other states, international institutions, and the international community as a whole.
Within the framework of the US legal system, the President will often be the first to interpret rules of international law. But if there is one clear principle of the separation of powers in the US constitutional system, it is that the interpretation of applicable law by the courts is determinative with respect to any dispute properly before them. It makes no difference whether the applicable law is derived from legislation, executive acts, common law, international law, or any other recognized source of law.
The US Executive has the exclusive power to negotiate treaties. It is vested with the exclusive power to consent to be bound by treaties on the international plane. It has the capacity to attach to its expression of consent reservations, understandings, and declarations. It is the lead voice in expressing consent to other rules of international law on behalf of the United States. But its power to interpret international law, just as with all other rules of law, is not exclusive, and cannot be given primacy in matters properly before the courts without violating a basic principle of the separation of powers.
Federalism and the roles of the constituent states
The constituent states of the United States assuredly have a lead role in implementing international obligations that fall within their broad remit. The US recognizes this whenever it appends a federalism understanding to its instruments of ratification. But to say that they have a lead role in implementation, and that they have broad discretion in the manner of implementation, does not mean that they have the option not to implement.
It is well recognized that the states have a valuable role to play as laboratories for experimentation. This is all the more the case for countries across the globe, which represent a much broader spectrum of diversity. International institutions are frequently mandated to glean best practices from this broad array. International law values and accommodates this diversity, and there is no reason to fear that it would hamper this cultivation of best practices.
As noted above, the difference in views appears to me to be one of setting the default position. In line with the design of the US Constitution, the intent of the framers, the common sense presumption that the US intends to comply with its international obligations, the promotion of US interests, and the recognition that the default position can always be overcome by legislative and executive action, that position should be one that facilitates compliance, not one that hinders it.
 Foster v. Neilson, 27 U.S. 253, 254 (1829).
 This refers to ordinary federal law. It does not include rules of U.S. constitutional law, which would override any inconsistent rule of international law within the domestic legal system.