The National Security Agency scandal shows no signs of losing steam, with the recent revelations about agency snooping on the leaders of U.S. allies. Even Senate Intelligence Committee Chair Dianne Feinstein, D-Calif., recognizes the need for a major probe of the nation’s electronic surveillance programs.

But the NSA’s scope has grown under the supposed supervision of Sen. Feinstein, her committee and their counterparts in the House. She is too close to the intelligence community to provide the required impartiality.

The same conflict affects the executive branch investigations of NSA launched last summer by President Barack Obama.

An independent investigation is required to address mounting revelations about the unsupervised and unauthorized activities of the NSA, beginning with its collection of bulk telephone data on all Americans, proceeding to its use of this data without court approval, and culminating in the president’s assertion that he did not know it was listening to the phones of German Chancellor Angela Merkel and other allied foreign leaders.

The last time the intelligence community was enmeshed in a comparable scandal was during the 1970s, when independent House and Senate committees, headed by Rep. Otis Pike, D-N.Y., and Sen. Frank Church, D-Idaho, held hearings on highly questionable CIA activities. Those hearings led to the establishment of the House and Senate intelligence committees as part of a new structure, including a special federal intelligence court, designed to keep the spy agencies under the rule of law.

Now that it has been shown that the structure created in the 1970s has failed to control the activities of NSA, the president and Congress should create a national commission, along the lines of the one that investigated the Space Shuttle Challenger disaster, to conduct an independent investigation into the NSA disaster. By law, an investigation would have to be conducted under wraps, but any breaches of law it uncovers could be made public. And it could make recommendations for improving intelligence oversight and accountability.

In 1976, Sen. Church gave the following explanation for ensuring that the NSA must operate under the rule of law, with full accountability. It is as relevant today as it was 37 years ago:

“In the need to develop a capacity to know what potential enemies are doing, the United States government has perfected a technological capability that enables us to monitor the messages that go through the air. Now, that is necessary and important to the United States as we look abroad at enemies or potential enemies. We must know, at the same time, that capability at any time could be turned around on the American people, and no American would have any privacy left — such is the capability to monitor everything — telephone conversations, telegrams, it doesn’t matter. There would be no place to hide.

“If this government ever became a tyrant, if a dictator ever took charge in this country, the technological capacity that the intelligence community has given the government could enable it to impose total tyranny, and there would be no way to fight back because the most careful effort to combine together in resistance to the government, no matter how privately it was done, is within the reach of the government to know. Such is the capability of this technology.

“I don’t want to see this country ever go across the bridge. I know the capacity that is there to make tyranny total in America, and we must see to it that this agency and all agencies that possess this technology operate within the law and under proper supervision so that we never cross over that abyss. That is the abyss from which there is no return.”

The nation’s leaders should heed Sen. Church’s prescient words.

An accounting is essential.

So is restraining the NSA.