In 1978, congressional investigations revealed that the NSA had spied on civilian anti-war protesters during Vietnam. The response was the Foreign Intelligence Surveillance Act. To prevent future abuses, the act drew a line between foreign intelligence and domestic law enforcement. The NSA was free to spy abroad, but when its agents wanted to wiretap in the United States, they had to ask a secret FISA court for a warrant. It was easy enough to get the warrants: Officials had to show probable cause that the person they were after was an agent of a foreign power. And the court, comprised of a rotating panel of federal judges chosen by the chief justice of the Supreme Court, almost never rejected an application. Governed by FISA, the supposedly rehabilitated NSA quietly went back to work. On the rare occasions over the last three decades when NSA directors have spoken publicly, it has been to offer assurances that the agency does not spy on U.S. citizens.

The problem was that with FISA under its belt, Congress effectively let the TV be the babysitter. Legislators relied on the new law to do the work, and oversight of electronic intelligence-gathering fell into serious decline. The justifiable secrecy surrounding eavesdropping became a bureaucratic carte blanche, and the NSA refused to produce hard information to back up its generic assurances that it was not abusing its powers. In the Reagan years, Rep. Norman Mineta, D-Calif., who served on the House intelligence committee, neatly summarized the relationship between the spies and the committee: "We are like mushrooms. They keep us in the dark and feed us a lot of manure."

Two years before Sept. 11, members of the House intelligence committee asked the NSA's general counsel for the internal legal guidelines that governed eavesdropping on the conversations of U.S. citizens. The agency stonewalled—not a good sign. The NSA's flimsy excuse was a Procrustean extension of attorney-client privilege, whereby any document that happened to be sitting on the desk of an NSA lawyer did not have to be handed over to Congress. The aftermath of Sept. 11 might have prompted greater oversight of electronic intelligence-gathering. After all, one of the major conclusions of both the bicameral congressional investigation and the 9/11 Commission was that Congress had been lax in that oversight. But after decades of keeping Congress at arm's length, the 9/11 Commission members were a piece of cake for the NSA. Despite its manifest size and resources, and its failure to hear so much as a whisper about al-Qaida's 9/11 operation, the agency merited only a few fleeting references in the commission's 500-page report.

After 9/11, the first sign that the NSA was overreaching on eavesdropping came when the famously circumspect FISA court took the unprecedented step of publishing a 7-0 decision in May 2002. The court, which approved about 10,000 warrant applications between the passage of FISA and Sept. 11, 2001, rebuked the Justice Department and the FBI for giving it wrong information in 75 post-9/11 applications for search warrants and wiretaps. The FISA judges called for stricter policing of FISA's delineation between domestic law enforcement and foreign intelligence operations to "protect the privacy of Americans in these highly intrusive surveillance searches."

Then-Attorney General John Ashcroft appealed, and it emerged that in the years since FISA was passed in 1978, a second secret judicial body—the FISA court of appeals—had been lurking in the wings. The Washington Post called this three-judge panel "a kind of ghost within the American judiciary"—one that had the peculiar distinction of never having had occasion to convene. Why not? Because it was established "to review the denial of any application" to the FISA court. And the court didn't deny applications.

The following year, as Washington began its full-court press for an invasion of Iraq, the NSA launched a surge of eavesdropping on delegates to the U.N. Security Council in New York. The operation was revealed when an English eavesdropper leaked an NSA e-mail requesting British assistance in the effort. It was a front-page story in Europe and around the world, but the American press didn't run with it, showing a level of deference to NSA secrecy matched only by Congress. Nevermind that the eavesdropping took place in Manhattan and violated the General Convention on the Privileges and Immunities of the United Nations, the Headquarters Agreement for the United Nations, and the Vienna Convention on Diplomatic Relations, all of which the United States has signed.

More dramatic—and also largely overlooked—was the disclosure last spring during John Bolton's confirmation hearings that the NSA was giving policy-makers and other intelligence agencies information about U.S. citizens. Since 1978, the NSA has insisted that when it intercepts a communication between a targeted foreigner and a nontargeted American it will redact the name of the American from the resulting intelligence report. The redactions are made to protect the privacy of the individual who was not the target, and to satisfy the Constitution's prohibition of warrantless searches. Yet at his hearings, Bolton admitted that on several occasions while he was an undersecretary of state he had asked the NSA to reveal the names of Americans in agency intercepts. The NSA obliged without any showing of cause or process of review. Newsweek investigated and learned that during one 18-month period in 2004 and 2005, the NSA supplied the names of 10,000 U.S. citizens to interested bureaucrats and spies.

That violation is arguably more egregious than the new revelations of warrantless eavesdropping. It involved vastly more people. (Bush's warrantless eavesdropping reportedly targeted between 500 and 1,000 people a year.) And it was an informal practice, without even the thin legitimacy of a secret executive order.

To be sure, the Times story is a bombshell. And if President Bush and Alberto Gonzales continue to argue that warrantless eavesdropping was justified under the authority granted by Congress after Sept. 11, this story will be an important chapter in the narrative of the Bush administration's promotion of executive power. But the shock—shock—professed in Congress and on editorial pages that a U.S. intelligence agency would exceed its mandate and play fast and loose with statutory and constitutional curbs? That seems at best naive and at worst a too-little-too-late gesture by the very people who should have seen this coming. Bush's executive order authorizing the NSA wiretaps is just the latest iteration (and not even the latest: See today's story about the FBI's surveillance of an Indianapolis Vegan Community Project) in a consistent pattern of inadequate oversight of legally questionable eavesdropping operations.

In 2002, then-director of the NSA Michael Hayden took the unusual step of asking for more debate about what his agency should and should not be able to do. "What I really need you to do," he told Congress, "is to talk to your constituents and find out where the American people want the line between security and liberty to be." That debate did not occur, and to judge by events and revelations in the intervening years, the agency—and the White House—interpreted the absence of protest as a vote of confidence and erred on the side of security. Now the talking heads are talking and a congressional inquiry is planned for January. Four years later, Michael Hayden may get his answer.

Related in Slate

Who's afraid of the FISA court? In 2002, Dahlia Lithwick detailed why we all should be. In 2001, Stewart Baker and Eugene Volokh discussed the fate of civil liberties in wartime. In 2004, Fred Kaplan addressed what transpires when allies spy on allies. In April, Daniel Engber explained how to tell apart the various post-9/11 commissions investigating intelligence failures.