For excellent background on this case, see this October 2007 essay by Andy McCarthy. Here I’ll provide a selective summary of Chief Justice Roberts’s majority opinion:
1. The judgment rendered by the International Court of Justice in the Avena case is not directly enforceable as domestic law in state or federal courts. (Slip op. at 7-27.)
a. No one disputes that the ICJ’s decision in Avena constitutes an international law obligation on the part of the United States. The question is whether it has automatic domestic legal effect such that it applies in state and federal courts.
b. There is a longstanding distinction between treaties that automatically have effect as domestic law (“self-executing” treaties) and those that, while they constitute international law commitments, depend upon implementing legislation by Congress for domestic effect (“non-self-executing” treaties). (Slip op. at 8-9.)
c. By signing the Optional Protocol on the Vienna Convention on Consular Relations, the United States agreed to submit disputes arising out of the Convention to the ICJ. But submitting to jurisdiction and agreeing to be bound are two different things. The most natural reading of the Optional Protocol is as a bare grant of jurisdiction.
d. The obligation to comply with ICJ judgments comes from Article 94 of the UN Charter, which provides that each member “undertakes to comply” with an ICJ decision in any case in which it is a party. We agree with the Executive Branch that the phrase “undertakes to comply” is not an acknowledgment that an ICJ decision will have immediate legal effect in domestic courts but rather a commitment on the part of members to take future action through their political branches to comply with an ICJ decision. Under the UN charter, the sole remedy for noncompliance is diplomatic—referral to the UN Security Council, where the U.S. has a veto—not judicial. Noncompliance with an ICJ judgment has always been regarded as an option by American presidents and the Senate, and there is no reason to believe that they would have signed up for any other result. Automatic enforcement as domestic law would undermine the ability of the political branches to make the sensitive foreign policy decisions whether and how to comply with an ICJ judgment. (Slip op. at 11-15.)
e. The Executive Branch’s interpretation of a treaty is entitled to great weight.
f. The dissent’s multifactor approach to deciding whether a treaty is self-executing is “arrestingly indeterminate” and is “the equivalent of writing a blank check to the judiciary.” (Slip op. at 18-20.)
2. The President did not have authority to bind state courts to follow the ICJ judgment. (Slip op. at 27-37.)
a. The responsibility for transforming an international obligation arising from a non-self-executing treaty into domestic law lies with Congress’s exercise of its lawmaking powers, not with unilateral presidential action. (Slip op. at 30-35.)
b. The President’s effort to bind state courts cannot be justified under his foreign-affairs authority to resolve claims disputes with foreign nations. (Slip op. at 35-37.)