By a vote of 6 to 3, the court held that neither that international judgment nor the treaty itself was sufficient to overcome a Texas procedural rule barring multiple appeals.
Mr. Bush had asked the judicial system of Texas, the state he once served as governor, to help the government “discharge its international obligations” by giving a new hearing to the convicted murderer, José E. Medellín. The Texas Court of Criminal Appeals refused, in the decision the Supreme Court upheld on Tuesday.
The Supreme Court, in a majority opinion by Chief Justice John G. Roberts Jr., concluded that the treaty at issue, the Vienna Convention on Consular Relations, was not “self-executing” — that is, that it did not automatically become binding domestic law upon its ratification in 1969. Consequently, only the president and Congress working together to enact further legislation, and not the president alone, could make the treaty enforceable against the states, the court said.
“The president has an array of political and diplomatic means available to enforce international obligations,” Chief Justice Roberts said, “but unilaterally converting a non-self-executing treaty into a self-executing one is not among them.” He added, “It should not be surprising that our Constitution does not contemplate vesting such power in the executive alone.”
Mr. Medellín was tried and convicted in 1994 for the rape and murder of two teenage girls without being informed of his right to seek assistance from Mexican diplomats. Such notification to foreign nationals facing criminal charges is required by the Vienna Convention. By the time his lawyers raised the issue, after his conviction and direct appeals, the Texas courts held that it was too late.
Mexico eventually filed a lawsuit in the International Court of Justice, usually known as the World Court, on behalf of 51 Mexicans on death row in various states who had not received their Vienna Convention notification. The court, in The Hague, ruled in 2004 that the United States was obliged to have the cases reopened and reconsidered.
At that point, international law clashed with American concepts of federalism and the separation of powers. At the heart of the Supreme Court’s decision were the majority’s twin conclusions that the treaty alone could not bind the states and that decisions of the World Court were not automatically enforceable in the domestic courts of countries under its jurisdiction.
Chief Justice Roberts noted that Article 94 of the United Nations Charter, which governs the enforceability of World Court decisions, provides that “each member of the United Nations undertakes to comply with the decision” of the World Court in any case to which it is a party. The chief justice said that “undertakes to comply” suggests no more than a promise by a country to do its best.
In a dissenting opinion, Justice Stephen G. Breyer disagreed with that interpretation. He also said the majority had set too rigid a formula for deciding whether treaties were “self-executing.” He warned that the decision threatened to destabilize the country’s relations with treaty partners under dozens of pacts.
As a result of the decision, Justice Breyer said, “the nation may well break its word even though the president seeks to live up to that word and Congress has done nothing to suggest the contrary.”
The two other dissenters were Justices David H. Souter and Ruth Bader Ginsburg, who both signed Justice Breyer’s opinion.
Justice John Paul Stevens, while providing a sixth vote for the majority result, wrote separately and did not sign the chief justice’s opinion. “I think this case presents a closer question than the court’s opinion allows,” he said.
Justice Stevens said the “undertakes to comply” phrase should be understood as a promise to enforce a World Court judgment, through action by the political branches if necessary. He called Mr. Bush’s effort “commendable” and urged Texas to comply voluntarily.
The situation presented by the case, Medellín v. Texas, No. 06-984, will not repeat itself because after the World Court ruling, Mr. Bush withdrew the United States from the World Court’s jurisdiction over future Vienna Convention disputes.
Had the Texas courts been willing to reopen Mr. Medellín’s case, the question would have been whether the outcome of his trial would have been more favorable had he known at the time of his rights under the Vienna Convention.
Dana Perino, the White House press secretary, said Tuesday that while “we’re disappointed” by the Supreme Court decision, the case had a “narrow focus” and should not be seen as representing a loss of presidential authority.