If the commission studying the 9/11 attacks is to have any hope of regaining its credibility -- of rising above the "partisan mudslinging" that House Majority Leader Tom DeLay rightly notes is tainting its work - Commissioner Jaime Gorelick must step down.

To see why, take a closer look at the defense she recently wrote for The Washington Post about her role on the 9/11 Commission and its conflict with her former role as deputy attorney general in the Clinton administration.

Gorelick appropriately points out that the original rules about the "wall" between law enforcement and intelligence agencies (a series of procedures designed to restrict the flow of information between the two) were put in place under Presidents Reagan and George H.W. Bush. No bombshell there. The Foreign Intelligence Surveillance Act - the law requiring the rules - wasn't adopted until 1978. Only as Reagan's presidency began did the Act, and court opinions interpreting it, begin to have real impact.

But the "wall" passed along to the Clinton administration underwent dramatic remodeling three years later.

Remarkably, Gorelick's defense ignores her own role in raising the "wall" higher than it had been in the prior administrations. One can read her spirited defense without learning that the 1995 memo she authored forbade CIA and FBI agents from freely exchanging information.

The rules she instituted (later made department policy) separated criminal investigations from intelligence gathering. As the memo itself said, these rules went "beyond what is legally required." In particular, the new rules prohibited any "'proactive' investigative efforts or technical coverages" of terrorist suspects on U.S. soil. In other words, under the Gorelick memo, our law enforcement and intelligence agencies were prohibited from any undercover work related to terrorist suspects.

We can debate the significance of Gorelick's rules. Where critics may see an important change, her defenders - like the commissioner herself - will see merely another, unremarkable link in a chain of events. There can be little doubt however, that Gorelick's actions are part of that chain.

Thus, even more problematic is Gorelick's response to critics who believe she has a conflict of interest in examining the Justice Department's response to 9/11 - her bland vow to recuse herself from questioning any of the friends she worked with in the Clinton administration.

But conflicts of interest are not based upon personal relations or temporal factors. As Gorelick surely knows, conflicts of interest in the legal world are subject-specific: They relate to a particular topic or issue, and they last forever. Someone who witnesses an event or who, as an attorney, provides advice for a particular transaction is forever barred from serving as a juror in the same case. It doesn't matter if that person has a spotless reputation for probity and fair play; the bar against sitting in judgment on that issue is absolute.

The passage of time doesn't change the fact that Gorelick helped raise the "wall" between law enforcement and intelligence; and that the higher wall was wrong. The 9/11 Commission is trying to determine the effects of that wall. And we now know that Gorelick is at least as "responsible" (if we are assigning responsibility) for the wall as Attorney General John Ashcroft. We would find it unacceptable for Ashcroft to sit on the 9/11 Commission, wouldn't we? So why should Gorelick?

Commissioner Gorelick's dismissive response to these concerns is disturbing. In time-honored Washington fashion, she and her fellow commissioners have circled the wagons, rejecting public scrutiny. Chairman Thomas Kean has gone so far as to tell the American public to butt out. "People," he said, "ought to stay out of our business."

For a commission interested in maintaining credibility or at least the appearance of impartiality, that's the wrong answer. And so is the incessant politicization of its work.

There is still time for the 9/11 commissioners to restore their credibility and make a strong, positive contribution to America's long-term strategy against terrorists. But to do so, they must take immediate steps to cure the image of partisanship that has begun to coalesce in people's minds. It must cease treating terrorism as political football.

And to assure the American people that the commission will leave no stone unturned, Gorelick must resign and be called to testify publicly about her own conduct. That conduct is now at issue - and she must not be allowed to serve as a judge in her own case.

Paul Rosenzweig is a senior legal research fellow in the Center for Legal and Judicial Studies at The Heritage Foundation and adjunct professor of law at George Mason University. Trent England is a Legal Policy Analyst for The Heritage Foundation.