Last week’s execution of Edgar Arias Tamayo aggravated an ongoing struggle of wills between Texas and its southern neighbor.Tamayo was convicted and sentenced to death for the brutal 1994 murder of a Houston police officer, and for nearly two decades his case wound its way through the U.S. justice system.Last week, the U.S. Supreme Court denied a motion to stay the execution, and his sentence was carried out in Huntsville. What drew the attention of the Mexican government and the State Department was that Tamayo was a Mexican national who, on arrest, was not advised of his right to access a home country consul — a right granted by an international treaty to which the U.S. is a party. But the treaty’s application in the States has a complicated history, and on many occasions it is not observed. In 2003, Mexico sued the U.S. in the U.N. International Court of Justice for violating the treaty. The following year, the international court ruled that the 51 Mexican nationals on Death Row across the U.S. at the time were entitled to judicial hearings to determine if their rights had been violated. In an effort to comply with the court, President George W. Bush directed states to review the relevant cases. But Texas would not relent. The issue reached the U.S. Supreme Court, which ruled that the president lacks authority to require states to comply with the treaty. Only an act of Congress could enforce the decision of the international court or the terms of the treaty. Such an act was introduced in 2011 but languished in the Senate.Tamayo’s case is the not the first to arouse international furor, nor will it be the last. Eleven Mexican nationals are on Death Row in Texas, according to the state Department of Criminal Justice website, including one scheduled for execution in April. The scope of international law is and should be limited, especially as it applies to individual states. But cases such as Tamayo’s raise reasonable questions about the nation’s obligations to international treaties and legitimate concerns about equitable treatment of similarly situated U.S. citizens abroad. Still, the Supreme Court was clear: If the U.S. government wishes to avoid these international flare-ups, the onus is on Congress to act, not on states to voluntarily comply.