COLUMBUS, Ohio — The botched execution of an Oklahoma inmate is certain to fire up the debate over what constitutes cruel and unusual punishment — the phrase written into the U.S. Constitution and defined by the courts, piece by piece, over two centuries.

Convicted killer Clayton Lockett, 38, began writhing, clenching his teeth and straining to lift his head off the pillow Tuesday evening after he was supposedly rendered unconscious by the first of three drugs in the state’s new lethal injection combination.

The execution was halted, and Lockett died of a heart attack about a half-hour later, authorities said.

While officials later blamed a ruptured vein — not the drugs themselves — the case is raising questions about the ability of states to administer lethal injections that meet the Eighth Amendment requirement that punishments be neither cruel nor unusual.

Death penalty opponents such as the American Civil Liberties Union called for moratorium on capital punishment. And the White House said the procedure fell short of the humane standards required when the death penalty is carried out.