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.”

Gov. Greg Abbott urged the Texas Supreme Court to block Robert Roberson from testifying before a House panel, arguing lawmakers in the committee are effectively usurping state clemency power left solely to him by subpoenaing the death row inmate.