Lawfare Archive: Orin Kerr on the Digital Fourth Amendment

In this archived episode of The Lawfare Podcast, Jack Goldsmith interviews Orin Kerr, Stanford Law School professor and leading expert on digital privacy law, about Kerr's book *The Digital Fourth Amendment: Privacy and Policing in Our Online World*. The conversation explores how the Fourth Amendment—originally designed for a physical, pre-digital world—has struggled to keep pace with rapid technological change. Kerr introduces his central theoretical framework, 'equilibrium adjustment,' which describes how the Supreme Court has historically responded to new technologies by modifying Fourth Amendment rules to restore a balanced level of government power and individual privacy. Using landmark cases like *Katz v. United States* and *Carpenter v. United States*, Kerr illustrates how the Court has adjusted doctrine to prevent either excessive government surveillance or an inability to enforce the law. The discussion delves into the challenges of applying these principles to modern issues such as geofence warrants, cell site location data, mosaic theory, and the government’s purchase of private data. Kerr argues that while some areas like cell site tracking may warrant protection, others—such as data bought on the commercial market—do not yet constitute a sufficient 'seismic shift' to trigger constitutional protection. He also reflects on the unique relationship between legal scholarship and judicial decision-making in this evolving field, where judges actively engage with academic work to navigate complex, precedent-shaping questions. The episode concludes with Kerr’s reflections on writing a comprehensive book that synthesizes decades of scholarship into a cohesive vision for the future of digital privacy law. Key takeaways include: (1) The Fourth Amendment must evolve through 'equilibrium adjustment' to maintain a balance between law enforcement power and individual privacy in the digital age; (2) The Supreme Court’s decision in *Carpenter* was a landmark equilibrium adjustment, but its factual assumptions about precision tracking have not fully materialized; (3) Mosaic theory—protecting privacy based on the cumulative effect of surveillance—is too vague and unworkable for consistent legal application; (4) The government’s purchase of private data from third parties does not currently constitute a Fourth Amendment violation due to insufficient evidence of a systemic power shift; (5) The good faith exception to the exclusionary rule severely limits doctrinal development by discouraging defense attorneys from raising novel Fourth Amendment claims. Overall, the episode presents a compelling case for proactive, principled legal adaptation to technology, grounded in the enduring values of privacy and balanced policing.