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There has been much speculation about how the Obama administration will deal with what many view as the Bush administration's harsh, abusive and illegal interrogation program. Some have called for an investigation by Congress or the Justice Department, possibly leading to criminal sanctions. Others think such investigations are infeasible or would smack of political retribution, proposing instead that a bipartisan commission look into the matter.

These are all bad ideas. They would bring little benefit, and they would further weaken the Justice Department and the CIA in ways that would compromise our security. (I worked at the Justice Department from 2003 to 2004 on issues that probably would be subject to new investigations, so readers should consider my views accordingly.)

To begin with, all of the relevant facts -- who approved what, what the legal opinions say and what actually happened -- are well known inside the government. The interrogation and related programs have been extensively scrutinized in public sessions of Congress, in many classified sessions by congressional intelligence committees, in several investigations by the CIA inspector general and the Justice Department's Office of Professional Responsibility and by the special prosecutor investigating the destruction of interrogation tapes.

These investigations were politically necessary, and the Obama administration should let them continue. When they are complete, the administration should disclose the facts and documents (including legal opinions) that can be made public without jeopardizing national security. To be credible, the disclosures should include information on the assenting role of congressional leadership as well as Clinton-era actions and legal opinions on issues such as rendition and targeted killing that were precursors to what the Bush administration did.

But we should also recognize the costs of these investigations. Second-guessing lawyers' wartime decisions under threat of criminal and ethical sanctions may sound like a good idea to those who believe those lawyers went too far in the fearful days after Sept. 11, 2001. But the greater danger now is that lawyers will become excessively cautious in giving advice and will substitute predictions of political palatability for careful legal judgment.

This was a serious problem before Sept. 11, and many believe it led to governmental structures and attitudes that precluded detection of the Sept. 11 plot. "I know from my work on this committee for the past 10 years that lawyers at CIA sometimes have displayed a risk aversion in the advice they give their clients," Democratic Sen. Bob Graham said during 2002 Senate intelligence committee hearings. Graham was typical then in complaining about "cautious lawyering" and in noting that "we are not living in times in which lawyers can say no to an operation just to play it safe."

The investigations and public recriminations of the past few years have led many government lawyers to be more risk-averse and politically sensitive than ever. They have also had a harmful effect on the lawyers' clients, especially in the CIA. In response to the many investigations, CIA officials are "lawyered up" and are drawing down their legal liability insurance. None of these officials is likely to go to jail. But the ordeal of answering subpoenas, consulting lawyers, digging up and explaining old documents, and racking one's memory to avoid inadvertent perjury is draining, not to mention distracting, for those we ask to keep the country safe.

And worse, it has spooked the intelligence community. When the CIA was asked to engage in aggressive tactics early in the Bush administration, it knew from bitter experience that the political winds would change and that it might be subject to "retroactive discipline." And so it sought approval from the president and his Cabinet, informed congressional leadership many times about what it was doing and got what it thought were airtight legal opinions from the Justice Department.

But these safeguards failed, and the CIA is once again mired in investigation and controversy. The lesson learned by many at the agency is that politically sensitive counterterrorism actions should be avoided, even if they are deemed legal and even if they have the express approval of political officials. We are going to be living with this skittishness for a long time, to the detriment of our security.

Yet another round of investigations during the Obama administration, even by a bipartisan commission, would exacerbate this problem. It would also bring little benefit. The people in government who made mistakes or who acted in ways that seemed reasonable at the time but now seem inappropriate have been held publicly accountable by severe criticism, suffering enormous reputational and, in some instances, financial losses. Little will be achieved by further retribution.

The best way for the Obama administration to establish a record of what happened under President Bush without further debilitating our national security system is simply to let the many current investigations run their course.

Jack Goldsmith, a Harvard Law School professor, is the author of "The Terror Presidency" and a member of the Hoover Institution Task Force on National Security and Law. From 2003 to 2004, he served as assistant attorney general in the Justice Department's Office of Legal Counsel. He wrote this article for the Washington Post.