It is April of 1970. President Richard Nixon, frustrated with the Vietnam War, orders tens of thousands of US and South Vietnamese troops to invade neutral Cambodia. He launches his new war–and widens his bombing campaign–without consulting an outraged Congress. Demonstrations engulf campuses and cities. Aides to National Security Adviser Henry Kissinger quit in protest. And at the Justice Department, an assistant attorney general named William Rehnquist, in charge of the Office of Legal Counsel, makes a case for the legality of Nixon’s new war in a white paper, “The President and the War Power.”

It is half a lifetime from that spring to this one, and half a world from Cambodia to Iraq. The historical chasm abruptly collapsed, though, with the release of the memo on torture written for the White House in August 2002 by Assistant Attorney General Jay Bybee, Rehnquist’s latter-day successor at the Office of Legal Counsel. What do Nixon and Cambodia have to do with the beatings and rapes at Abu Ghraib? Ask Bybee, because it is his memo that makes the comparison with Cambodia and Rehnquist, a comparison that lays open the deeper motivations, goals and implications of the Bush Administration’s interrogation policy.

The Bybee memo attempts to erect a legal scaffolding for physical and psychological coercion of prisoners in the War on Terror. Coming from the Office of Legal Counsel, it holds the authority of a policy directive. The memo proposes so finessed and technical a reading of antibrutality laws that all manner of “cruel, inhuman or degrading” interrogation techniques–including beatings and sexual violations like those in Abu Ghraib–simply get reclassified as Not Torture. The memo’s language so offends common sensibility that within a few days of its release, White House officials were disavowing its conclusions and selectively declassifying documents allegedly showing the President’s commitment to humane treatment of prisoners.

(How exculpatory is the Bush Administration’s self-serving document dump? Not a single page is concerned with prisoners in Iraq. Not one sentence refers to the CIA, which according to Seymour Hersh first employed coercive interrogation in Afghanistan with the acquiescence of Defense Secretary Donald Rumsfeld. Indeed, the most substantial and authoritative Pentagon document declassified by the White House, the April 4, 2003, “Working Group Report on Detainee Interrogations in the Global War on Terrorism,” explicitly limits its scope to “DOD personnel in DOD interrogation facilities.” Contract interrogators and CIA operatives are nowhere covered; neither are prisoners held under the authority of foreign governments, paramilitary allies or US intelligence agencies.)

Yet even while putting up a smokescreen of concern for humanitarian treatment of prisoners, the Administration made no attempt to distance itself from Bybee’s most crucial theme: unreviewable presidential war powers. Anti-torture laws, the memo argues, simply do not apply to “detentions and interrogations of enemy combatants pursuant to [Bush’s] Commander-in-Chief authority.” All the documents released by the White House reflect this same obsession with presidential war powers-and in many cases, incorporate Bybee’s precise language.

It is in defense of his view of the Commander in Chief’s legal impunity that Bybee invokes the Cambodia precedent, citing Rehnquist’s 1970 white paper as his principal authority. Rehnquist spelled out his arguments both in that memo and in an article later that year for the New York University Law Review.

One glance at the Rehnquist documents and it is easy to see why his 1970 reasoning resonates throughout the Bush Administration’s 2002 and 2003 memorandums. Just as Bybee finds that torture isn’t torture, Rehnquist argued that the invasion of Cambodia wasn’t really an invasion: “By crossing the Cambodian border to attack sanctuaries used by the the enemy, the United States has in no sense gone to war with Cambodia.” The Bybee memo offers officials accused of torture the “necessity” defense; in 1970, Rehnquist argued that pursuing Vietcong troops into previously neutral territory was “necessary to assure [American troops’] safety in the field.”

In particular, Rehnquist offered the Nixon White House a bold vision of the Commander in Chief’s authority at its most expansive and unreviewable: The President’s war power, he wrote acerbically, must amount to “something greater than a seat of honor in the reviewing stand.” Cambodia–where the devastation of the war and the Nixon Administration’s carpet-bombing following the invasion would prepare the way for the Khmer Rouge holocaust–amounted to “the sort of tactical decision traditionally confided to the commander in chief.”

For Rehnquist, the invasion of Cambodia in May of 1970 was a dual watershed. On the one hand, it marked the greatest assertion of expansive presidential warmaking power, crystallized in the white paper cited by Bybee. At the same time, protests against the Cambodian invasion led Nixon to centralize the gathering of domestic political intelligence directly in the White House; Rehnquist supported this domestic expansion of executive-branch authority, arguing in court for no-knock entry, preventive detention, wiretaps and other ancestors of today’s Patriot Act.

The authority of Nixon and his successors was soon curtailed–at least on paper–by reform-minded legislation: the War Powers Act, the Freedom of Information Act, CIA reform, the War Crimes Act and a host of other statutes. And ever since the invasion of Cambodia, a parade of conservative policy-makers–among them Rehnquist, Rumsfeld and Vice President Dick Cheney–have repeatedly sought to regain the expansive presidential power asserted in Rehnquist’s memo.

This is what is really at stake in the torture scandal. The circle of history has come around: The Bush Administration’s theory of unconstrained war powers connects straight back to its Nixonian origins. On Monday, Chief Justice Rehnquist, true to form, dissented from the Supreme Court’s ruling granting Guantánamo Bay prisoners access to US courts, although even Rehnquist drew the line at indefinite and unreviewable imprisonment of an American citizen in the Hamdi case. Rehnquist may today awkwardly parse the outer limits of military detention. But there is no doubt that his career-long crusades, rooted in the Nixon presidency, on behalf of gloves-off policing practices and executive-branch warmaking prerogatives now come together in a Baghdad prison. The Bush Administration’s memos not only facilitate torture as public policy. Like the Nixon Administration in 1970, they articulate a philosophy of the presidency best described as authoritarian. That is the hidden message of Abu Ghraib.