With his execution looming last Thursday, the 57-year-old Texas death row inmate watched as his attorneys’ legal arguments were rejected in the courts and his pleas for clemency disregarded, as the state parole board declined to recommend he receive a lesser sentence or reprieve.

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.”