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.”

Until Monday, the Texas governor had not publicly shared his thoughts on the actions of a bipartisan group of lawmakers that stopped Roberson's scheduled execution.