Mass surveillance programs - collecting metadata and communications at scale - are effective tools for preventing terrorism.

In the fall of 2001, American civics teachers faced an unusual pedagogical challenge. The September 11 attacks had upended assumptions about national security, and students wanted to know what the government was doing to prevent another attack. The answer, as it emerged over the following weeks and months, centered on information. The more the government could collect about communications, the argument went, the better it could identify threats before they materialized. This logic underpinned the USA PATRIOT Act, signed into law on October 26, forty-five days after the attacks, which dramatically expanded the government's authority to collect intelligence on Americans. Section 215 of the Act allowed the government to obtain "any tangible things" relevant to a terrorism investigation. Civics curricula described these authorities as both necessary and effective, a reasonable trade between privacy and security in an age of networked terrorism.

The classified programs built on these authorities operated in secrecy for more than a decade. In June 2013, Edward Snowden, a contractor working for the National Security Agency, released thousands of documents to journalists Glenn Greenwald and Laura Poitras. The revelations described a bulk telephone metadata collection program that gathered information on nearly every phone call made in the United States. The NSA did not record the content of conversations, but it did collect who called whom, when, and for how long. Similar programs operated for internet communications. The scale was far beyond what Congress or the public had understood when the PATRIOT Act was passed. This was not targeted surveillance of suspected terrorists. It was wholesale collection of data on Americans, stored and analyzed in case it became useful later.

The question that followed was whether the programs worked. The NSA and its defenders argued that bulk collection had contributed to counterterrorism investigations, though they could cite few cases where it had been decisive. Multiple post-Snowden reviews examined the classified evidence and reached similar conclusions. The Privacy and Civil Liberties Oversight Board, an independent agency created by Congress, released a detailed report in 2014. It found that the Section 215 bulk telephone records program had not been essential to preventing any terrorist attack. The Board reviewed the government's classified assessments and concluded that in the few cases where the program had contributed information, that information could have been obtained through conventional investigative tools. The Board went further, finding that the program "lacks a viable legal foundation under Section 215" and recommending it be shut down. A separate review group appointed by President Obama found similar limitations, noting that the bulk collection program was "not essential to preventing attacks."

The NSA's response was telling. Officials did not argue that the program had stopped dozens of plots. Instead, they contended that metadata analysis had provided useful context in investigations, even if it was rarely the key piece of evidence. This narrower claim was harder to evaluate, since much of the relevant information remained classified. But the sweeping effectiveness argument that had been taught in civics classes, that collecting everything made everyone safer, had been tested against the evidence and found wanting.

Congress ended the bulk telephone records program in 2015 under the USA FREEDOM Act, which required the government to obtain specific court orders for call records rather than collect metadata wholesale. The shift was significant not because it ended all surveillance, but because it represented a policy correction. The program that had been described as a necessary and effective security tool had been found, on examination, to be both legally questionable and of marginal operational value. The correction mattered less for what it changed immediately than for what it revealed about how security claims are made and tested. Effectiveness in counterterrorism, like effectiveness in medicine, requires evidence, not just plausibility.