“The EU embargo has slowed down, but not stopped executions,” Richard Dieter, executive director of the Death Penalty Information Center in Washington, D.C, told me. “It has made the states seem somewhat desperate and not in control, putting the death penalty in a negative light, with an uncertain future.”

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Lethal injection is by far the predominant method of execution in the United States. Before the drug shortage, virtually every lethal-injection protocol used the same three-drug method. A first drug, sodium thiopental, anesthetized the prisoner. Then a second drug, pancuronium bromide, paralyzed the inmate and halted his or her breathing. Finally, an injection of potassium chloride stopped the heart. Jay Chapman, an Oklahoma medical examiner with little pharmacology experience, first proposed the three-drug protocol in 1977. Asked about his qualifications by a New York Times reporter 30 years later, Chapman described himself as “an expert in matters after death but not in getting people that way.”

Texas became the first state to use lethal injection when it executed Charles Brooks, Jr. on December 7, 1982. Since then, U.S. states have executed over 1,000 death-row inmates by lethal injection. By the time the three-drug cocktail's constitutionality came before the U.S. Supreme Court in 2008 in Baze v. Rees, lethal injection had become the preferred method of execution for 36 states and the federal government. Thirty of those states used Chapman’s method. The U.S. Supreme Court upheld the three-drug protocol in a 7-2 decision.

The European Union, for its part, makes no secret of its death-penalty stance. EU guidelines call for its “universal abolition” and declare that doing so would “[contribute] to the enhancement of human dignity and the progressive development of human rights.” EU diplomats and leaders frequently petition U.S. governors and state parole boards to halt forthcoming executions. Sometimes, the supranational organization even works in more subtle ways: EU agencies contributed over $4.8 million in donations to U.S. anti-death-penalty organizations between 2009 and 2013.

The EU’s influence extends to the U.S. Supreme Court, where justices have drawn upon the organization's amicus curiae briefs from time to time in death penalty cases. Justice John Paul Stevens’ majority opinion in 2002’s Atkins v. Virginia cited the EU’s brief on worldwide opposition to executing the mentally disabled as a factor in the Court's decision to forbid the practice in the United States. During oral arguments for Roper v. Simmons in 2005, Justice Anthony Kennedy pondered whether European views should be considered when assessing the “unusual” aspect of the Eighth Amendment’s prohibition of “cruel or unusual punishment.” The EU had already told the Court in an amicus brief that imposing the death penalty on persons who were minors at the time of the crime “violates widely accepted human rights norms and the minimum standards of human rights set forth by the United Nations.”