As a constitutional matter, the Supreme Court has long held that, where an individual has a reasonable expectation of privacy, search and seizure may occur only once the government has obtained a warrant, supported by probable cause and issued by a judge. The warrant must specify the places to be searched and items to be seized.
There are exceptions to the warrant requirement. In 1979 the court held that the use of a pen register to record numbers dialed from someone’s home was not a search. The court suggested that people who disclose their communications to others assume the risk that law enforcement may obtain the information.
More than three decades later, digitization and the explosion of social-network technology have changed the calculus. In the ordinary course of life, third parties obtain massive amounts of information about us that, when analyzed, have much deeper implications for our privacy than before.
As for Section 702 of FISA, the Supreme Court has held that the Fourth Amendment does not protect foreigners from searches conducted abroad. But it has never recognized a foreign intelligence exception to the warrant requirement when foreign-targeted searches result in the collection of vast stores of citizens’ communications.