In his recently published book, former President George W. Bush admits that when asked to approve waterboarding, long considered torture under US and international precedents, his response was, "Damn right." This admission has created a difficult dilemma for President Obama and Attorney General Eric Holder.

Torture is a federal crime punishable by up to twenty years in prison. When President Nixon was forced to release a White House tape recording showing that he had orchestrated the cover up of the Watergate burglary, he immediately exposed himself to criminal prosecution and likely conviction for obstruction of justice. His successor, President Gerald Ford, quickly pardoned Nixon, who had resigned, to avoid that result. The pardon cost Mr. Ford his election.

President Obama has the power to pardon Mr. Bush. As with the Ford pardon, it would generate outrage among many Americans, and, in my opinion, would be wrong.

The other options facing President Obama and Attorney General are to do nothing or to enforce the anti-torture law by commencing a full and fair investigation of the facts by an independent prosecutor to determine whether criminal charges are warranted.

Under the US Constitution, the president is required to "faithfully execute the laws." It is hard to think of a more blatant confession of a crime than the one made by George W. Bush. To leave it unexamined is to reject the constitutional obligation and to create a corrosive sense that the law applies, when it does, only to lesser mortals, but not to higher-ups and certainly not to presidents. A dual standard of justice is intolerable in a democracy. Doing nothing, then, is not a constitutionally acceptable response.

There is another reason to investigate. The Convention Against Torture, ratified under Ronald Reagan, obliges our government to ensure "a prompt and impartial investigation" when there are "reasonable grounds to believe" torture has occurred (Article 12). To ignore former President Bush's admission is to disrespect our solemn treaty obligation.

It is not a sufficient justification for inaction to claim, as Attorney General Holder has in the past, that anyone acting on a basis of the notorious Torture Memos written by the former President's Justice Department (and later withdrawn) is free from prosecution. Those Memos purported to allow torture by contending -- incorrectly -- that a US president had the right to violate US criminal laws. They also concocted an absurd definition of torture. Torture, said the Memos, required a pain equivalent to the pain of death. But no one knows what the pain of death is, and the author of the Memos admitted that he didn't know either. Clearly, the definition was a sham and the Memos were a sham.

To suggest that these sham Memos -- a Justice Department official characterized them as "insane" on their face -- constitute a defense runs into big obstacles. The Convention against Torture permits "no exceptional circumstances whatsoever" to its absolute ban. That should mean there is no exception for torture committed on advice of counsel -- particularly the obviously faux advice of the Torture Memos. Reading an exception into the anti-torture statute, which is intended to carry out the treaty, would seriously derogate from our government's obligations to carry out the treaty.

More important, the Torture Memos were written under the auspices of the Bush White House itself, as part of a scheme to create immunity from criminal prosecution. To the extent that George W. Bush was part of that effort, he cannot claim protection from it--he cannot have relied on the Memos in good faith.

The Attorney General should not be the one to judge whether the Justice Department's discredited Torture Memos provide a complete defense to former President Bush. Because Mr. Holder has the reputation and clout of the Justice Department to uphold, he has a conflict of interest in determining what weight, if any, to give those Memos.

That is why he needs promptly to name a special prosecutor to decide whether the anti-torture act, or any other federal laws, were broken by former President Bush in authorizing the water boarding and torture.

Failing to act will cast a long shadow over the rule of law in America and our commitment to justice and accountability. No country should tolerate criminal impunity in its top officials, least of all the United States. President Obama himself has attacked the idea of impunity when talking about foreign governments.

Naming a special prosecutor to investigate whether there are grounds to charge former President Bush is the constitutionally, and morally, correct action to take. The ACLU and others are calling for this to happen. As long as the process is fair, lawful and professional, it is one that the country will accept whatever the results.