The Role of "Relevance" for the Scope of Government Surveillance

Federal Rule of Evidence 401 provides:

Evidence is relevant if:

(a) it has any tendency to make a fact more or less probable than it would be without the evidence; and

(b) the fact is of consequence in determining the action.

I pointed out in 1983 (I was not alone) that the test of whether evidence makes a fact in issue more or less probable to any degree is extremely liberal and that this liberal test, if taken literally, renders little if any evidence "irrelevant." I have also pointed out at various times (see, e.g., Sections 9 & 10, WIGMORE ON EVIDENCE (Tillers rev. 1983); again, I was certainly not alone in doing so) that elimination or dilution of the equivalent of a materiality requirement - the requirement that only evidence that bears on an issue that matters in the eyes of the substantive law - either eliminates or further dilutes the exclusionary force of the relevance requirement.
If the Wall Street Journal is to be believed, the FISA court opened the door to broad data collection by the federal government - almost unconstrained domestic data collection - by taking two steps:
adopting the equivalent of a literal interpretation Federal Evidence Rule 401's codification of the so-called logical relevance principle - the principle that evidence is relevant if it has any tendency to affect the probability of a fact in issue;
and
adopting (to boot) extremely broad characterizations of the factual questions (e.g., "terrorism") to which any sought-for evidence must be relevant.
See Valentino-DeVries & Gorman, Secret Court's Redefinition of 'Relevant' Empowered Vast NSA Data-Gathering (July 8, 2013):

Snippets:

"The National Security Agency's ability to gather phone data on millions of Americans hinges on a secret court ruling that redefined a single word: 'relevant.'

"This change—which specifically enabled the surveillance recently revealed by former NSA contractor Edward Snowden—was made by the secret Foreign Intelligence Surveillance Court, a group of judges responsible for making decisions about government surveillance in national-security cases. In classified orders starting in the mid-2000s, the court accepted that "relevant" could be broadened to permit an entire database of records on millions of people, in contrast to a more conservative interpretation widely applied in criminal cases, in which only some of those records would likely be allowed, according to people familiar with the ruling.

...

"'Relevant' has long been a broad standard, but the way the court is interpreting it, to mean, in effect, "everything," is new, says Mark Eckenwiler, a senior counsel at Perkins Coie LLP who, until December, was the Justice Department's primary authority on federal criminal surveillance law.

...

"Under the Patriot Act, the Federal Bureau of Investigation can require businesses to hand over 'tangible things,' including 'records,' as long as the FBI shows it is reasonable to believe the things are 'relevant to an authorized investigation' into international terrorism or foreign intelligence activities.

"The history of the word 'relevant' is key to understanding that passage. The Supreme Court in 1991 said things are "relevant" if there is a 'reasonable possibility' that they will produce information related to the subject of the investigation. In criminal cases, courts previously have found that very large sets of information didn't meet the relevance standard because significant portions—innocent people's information—wouldn't be pertinent.

"But the Foreign Intelligence Surveillance Court, FISC, has developed separate precedents, centered on the idea that investigations to prevent national-security threats are different from ordinary criminal cases. The court's rulings on such matters are classified and almost impossible to challenge because of the secret nature of the proceedings. According to the court, the special nature of national-security and terrorism-prevention cases means 'relevant' can have a broader meaning for those investigations, say people familiar with the rulings.

...

"Former Sen. Jon Kyl spoke on the floor of the Senate in favor of the 'relevance' standard. 'We all know the term "relevance." It is a term that every court uses,' he said in 2006. 'The relevance standard is exactly the standard employed for the issuance of discovery orders in civil litigation, grand jury subpoenas in a criminal investigation,' he said.

"But a few people cautioned that 'relevant' could be defined to the point of irrelevance. 'Relevance is a very broad standard that could arguably justify the collection of all kinds of information about law-abiding Americans,' former Sen. Russ Feingold said on the Senate floor in February 2006. He argued for stricter wording, and failed."

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