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.”

It’s rare for governors to step in to halt executions. In the case of Robert Roberson, it ended up being state lawmakers who took extraordinary steps.