Descent Into Madness.

The Justice Department memo released Thursday is a key link in the chain of evidence connecting the monstrous abuse of detainees at the Abu Ghraib prison and elsewhere straight to the White House.

President Bush has described the torture and murder of prisoners by U.S. military personnel as the work of an aberrant few. But this 2003 memo opened the door to precisely the kinds of abuse so horrifically chronicled in the Abu Ghraib photographs.

And the memo’s author — John Yoo, then a deputy in the Justice Department’s Office of Legal Counsel — was a longtime ally and notoriously pliant scribe for the radical legal views of Vice President Cheney and his chief enforcer, David S. Addington. Yoo’s memo is a historic document. It is the ultimate expression of Cheney’s belief that anything the president or his designates do — no matter how illegal, barbaric or un-American — is justifiable in the name of national self-defense.

It is also an example of how enabling zealots to disregard the rule of law and the customary boundaries of human conduct leads to madness.