The three-page letter sent Sunday by James Sullivan, Abbott’s general counsel, said only the governor has the constitutional authority to delay an execution. Sullivan warned that unless the court rejects the subpoena, “it can be repeated in every capital case, effectively rewriting the Constitution to reassign a power given only to the Governor.”

Robert Roberson, who had been set to be the first person in the U.S. to be put to death for a murder conviction tied to a diagnosis of shaken baby