The Fourth Amendment’s prohibition on unreasonable warrantless searches and seizures has been much in the news of late. Consider just a small sampling: The revelations of Edward Snowden about the National Security Agency’s surveillance programs, numerous high-profile cases involving police use of deadly force, and the Supreme Court’s two recent decisions requiring warrants prior to searching the cellphones of arrestees and accessing cell-site location data all implicate the Fourth Amendment. Also, in the recent past Congress has dramatically expanded and then dramatically narrowed the federal government’s search and seizure powers in the national security setting, while states have struggled with a range of domestic investigation issues, including limitations on drone surveillance, database searches, and DNA analysis.

The Fourth Amendment in Flux, by Michael Gizzi and R. Craig Curtis, is thus highly timely. Although the book does not discuss the recent cell-site case (Carpenter v. United States), which was decided two years after publication, it provides a useful account of the technology-oriented Supreme Court decisions that presaged it, and even comes close to predicting the outcome in Carpenter itself. The book also deals with a wide array of cases dealing with more traditional searches and seizures, such as stop and frisks, traffic arrests, home entries, drug testing programs, and the like. As its subtitle indicates, much of the book focuses on Supreme Court cases handed down between 2005, the year John Roberts became chief justice of the Court, and 2016, the year the book was published. But a good half of the book also describes many of the Court’s Fourth Amendment decisions in the preceding years, in particular those decided by the Courts presided over by Chief Justices Earl Warren (1952 to 1969), Warren Burger (1969 to 1986) and William Rehnquist (1986 to 2005).

Throughout the book the authors develop four basic points. First, they argue that the Roberts Court, and indeed all courts subsequent to the Warren Court, have endorsed a “crime control” jurisprudence that heavily favors law enforcement. In addition to canvassing the relevant case law, the authors provide the political backdrop that helps explain this jurisprudence, emphasizing the crime wave that accompanied the Warren Court years, the tough-on-crime attitude of every president from Richard Nixon through George W. Bush, and the way in which police have exploited the Court’s decisions (through, for instance, the pretextual, and often race-based, use of traffic stops). Second, the authors contend that, in those rare Fourth Amendment cases in which defendants prevail (approximately 25% of the total since 1970), the Court has generally avoided sweeping pronouncements, instead merely issuing “minor corrections” to previous decisions. Third, Gizzi and Curtis provide evidence that the membership of the Court matters. They point specifically to the additions of Justice Sonia Sotomayor and Justice Elena Kagan to the Court and the willingness of Justice Antonin Scalia to depart from his typical crime-control stance to explain why, in contrast to the Court’s record from 1970 to 2010, its more recent decisions have split almost evenly between the state and the defense. Finally, they suggest that one substantive reason for the “flux” mentioned in the book’s title is the advent of technology, such as Global Positioning System (GPS) tracking and cellphones, that enhances law-enforcement ability to discover private facts.

These observations about the Supreme Court’s recent jurisprudence are hard to dispute. In fact, in the two years since publication of the book, they remain very pertinent. The Roberts Court has decided 13 Fourth Amendment cases in that time. Continuing the countertrend noted by Gizzi and Curtis, roughly 50% (6 out of 13) have been decided for the defense. Furthermore, virtually all of the cases decided in favor of the government deal with the relatively tangential issue of qualified immunity—whether an officer can be held liable for the use of excessive force or for some other violation of the Fourth Amendment. At the same time, consistent with the book’s first theme, the one state-oriented case of the seven that did not involve the qualified immunity issue, Utah v. Strieff, significantly increases police power and the potential for racialized investigative actions. That case allows law-enforcement officers to arrest individuals on the basis of outstanding warrants, even if the initial stop of the individual is clearly illegal, a ruling that incentivizes the police to conduct such stops.

Furthermore, consistent with the book’s second theme, of the six cases decided between 2016 and 2018 that find for the defendant, most simply fine-tune rather than overturn precedent. For instance, the Court held that the state cannot force drivers suspected of drinking to submit to a warrantless blood test, but that it can require those drivers to take a breathalyzer. It also held that the automobile exception, which generally permits warrantless searches of cars, does not permit a warrantless search of a car that is parked in the defendant’s front yard. And it held that the driver of a rental car has Fourth Amendment protection against warrantless searches of the car even if his or her name is not on the rental agreement. None of these decisions is earth shattering (although, consistent with the authors’ third observation, all of them were either authored or joined by justices Sotomayor and Kagan.)

Finally, relevant to Gizzi and Curtis’s fourth point about the role of technology in creating judicial flux, one of the six pro-defendant cases decided since 2016 resulted in the aforementioned decision in Carpenter, where the police used cell–site location data to pinpoint the location of the defendant near the scene of four robberies. The government argued that this seizure of data did not implicate the Fourth Amendment, pointing to long-standing precedent establishing the so-called third-party doctrine—the idea that information that is “surrendered” to a third party (here the cellphone carrier) is not entitled to Fourth Amendment protection because one assumes the risk that such information will be turned over to the government. But the Court decided otherwise in a 5–4 opinion written by Chief Justice Roberts (and joined by Sotomayor and Kagan; Scalia had passed away two years earlier). As he had done in Riley v. California, the cellphone search case highlighted by Gizzi and Curtis, Roberts emphasized the huge amount of information that technology can provide the police, which in this case entailed over 150 days of location data. Carpenter could spell the beginning of the end for a precedent that has been a mainstay of the Court’s Fourth Amendment jurisprudence since at least the 1970s.

In short, recent case law confirms the validity of Gizzi and Curtis’s insights about the Roberts Court’s vacillating approach to the Fourth Amendment. Their book is clearly meant to focus on such generalities; it does not dissect the cases in the way that a law book might, nor does it attempt to advance an explanatory theory about the Fourth Amendment. Further, in a few places one can quibble with the accuracy of the authors’ case descriptions. But the important takeaway is that The Fourth Amendment in Flux is a highly readable and thoughtful account of Fourth Amendment law over the last half century.