It was only in 2002, when Jesselyn Radack disclosed that the prosecution of “American Taliban” John Walker Lindh had involved several violations of Lindh's constitutional rights, that the new wave of whistleblowing and public-accountability leaks reemerged. Thomas Tamm and Russ Tice each disclosed the Bush administration's warrantless-wiretap program to The New York Times; AT&T employee Mark Klein disclosed the company’s complicity in illegal wiretapping; and William Binney, Thomas Drake, and others challenged internally—and in Drake's case disclosed publicly—early aspects of NSA dragnet surveillance. Chelsea Manning disclosed a major document cache to WikiLeaks, driven by what she viewed as American forces’ callous disregard for civilian casualties and silent complicity in Iraqi government torture. Most critically, Edward Snowden's disclosures led to the introduction of dozens of bills in Congress, a judicial opinion, and two executive-branch independent reviews that demanded extensive reforms to surveillance programs.

As with the Vietnam-era leaks, the wave of accountability leaks in the past dozen years was the result of the national-security establishment overstepping its constitutional boundaries in a state of emergency. Reacting to the shock of 9/11, the national-security system responded as best it could. Some of the responses were measured and necessary. Others were abusive mistakes followed by aggressive cover-ups. The army ordered an inquiry into allegations of torture by military personnel, then forced out the general who dutifully reported the "sadistic, blatant and wanton" "systematic and illegal abuse" he found. The CIA embraced torture with a vengeance, lied about it to the administration and Congress, and went so far as to spy on its Senate overseers in its attempt to cover its tracks. The NSA built a surveillance apparatus that overstepped its statutory and constitutional authority, and in the process of normalizing that apparatus dragooned parts of the judiciary and Congress into providing a veneer of legitimacy to its actions. Viewed in this light, the war that President Obama and his attorney general have waged on whistleblowers can no longer be reasonably seen as simply a response to increased leaks in general. Instead, it reflects an increasingly embattled national-security system pushing deeper into barely defensible or indefensible constitutional dead ends and ramping up aggressive criminal prosecutions to defend itself from the ultimate failsafe for stopping abusive systems: individual conscience.

One thing is clear. Without the men and women of conscience who have come out over the past 12 years and disclosed aspects of the abuses, the system would have kept on grinding.

The single most important lesson of Snowden's disclosures is that even well-designed and well-intentioned systems of checks and balances become corroded and subverted over time. No matter how perfect a set of rules or an institutional or organizational system was when it was created, it cannot remain so in the face of time, change, and the pressures of new emergencies. The FISA system that emerged from the 1970s worked reasonably well in the latter stages of the Cold War, when it was grappling with the kinds of threats and the technological environment for which it was designed. But as Binney put it, everything changed after 9/11. The urgency of preventing another attack swept away the rules. Partly in response to heroic efforts of some insiders to change policies, and mostly due to the public exposure of the warrantless wiretapping program, elements of the judicial-oversight system were reintroduced starting in 2006, and Congress passed the FISA Amendments Act in 2008. But the practices that had developed had become so complex and diverse that the new oversight system was completely inadequate to contain them.