Since the US Supreme Court first addressed the death penalty the 1879 case Wilkerson v. Utah, the Court has struggled with determining the penalty's constitutional boundaries. In 1976 the court held in Gregg v. Georgia that the imposition of the death penalty does not always violate the Eighth Amendment's prohibition against cruel and unusual punishment. The Gregg opinion noted the court's seemingly less-than-consistent application of the Eighth Amendment in death penalty cases. This included the 1972 case of Furman v. Georiga, decided only a few terms prior to Gregg, where only a plurality of the Justices concluded that the penalty was constitutional. The court in Gregg sought to reconcile its position over time by emphasizing how the Eighth Amendment's protections are dynamic and demanded the recognition of evolving public attitude. In this context, the court provided a two-prong inquiry for determining the constitutionality of the death penalty: whether the penalty imposed will avoid causing unnecessary pain and suffering; and whether the penalty is proportional to the severity of the crime.
In Penry v. Lynaugh the court in 1989 decided the constitutionality of the death penalty when applied to a person with intellectual disabilities. The court sought guidance on the issue from state death penalty legislation pertaining to those persons, considering modern legislative efforts the best indicator of society's evolving standards. At the time of Penry, the court found no national consensus on prohibiting the execution of the mentally disabled. In part because of this survey, the court split 5-4 in holding that the execution of persons with intellectual disabilities did not violate the Eighth Amendment. Instead the majority held that a showing of intellectual disability served as a mitigating factor for the sentencing body to consider.
Public consensus on the execution of persons with intellectual disabilities continued to change in the years following the court's decision in Penry. When the issue came before the court again in Atkins v. Virginia in 2002. Justice Stevens, writing for the majority, channeled this consensus in finding the execution of persons with intellectual disabilities unconstitutional as it was cruel and unusual punishment. Justice Stevens addressed the actions by state legislatures to prohibit these executions post-Penry as support for stepping back from that decision. The Atkins decision left unanswered how to determine whether a person had an intellectual disability that precluded application of the death penalty.