The Aftermath of Carpenter v. United States

By Matthew Tokson

I recently wrote an article, "The Aftermath of Carpenter: An Empirical Study of Fourth Amendment Law, 2018-2021," forthcoming in the Harvard Law Review. The article looks at the state of Fourth Amendment law following the Supreme Court’s groundbreaking 2018 opinion in Carpenter v. United States. It analyzes hundreds of recent Fourth Amendment cases and identifies the factors that drive modern search decisions. It describes an emerging “Carpenter Test” that determines when the Fourth Amendment applies to government actions.

Essentially, this test looks to (1) the revealing nature of the data collected by the government, (2) the amount of data collected, and (3) whether a person has voluntarily disclosed their information to a third party. While other considerations sometimes arise, these three are the most influential and commonly used factors in modern Fourth Amendment decisions. They drive case outcomes in hundreds of frontier cases.

More broadly, courts have largely embraced Carpenter and its analysis, with almost no overt criticism and relatively little misapplication. The law is still developing, but Carpenter appears to be workable in the lower courts. That said, the aftermath of Carpenter highlights the surprisingly common phenomenon of “indirect noncompliance,” where courts intentionally misinterpret controlling precedent in order to reach a preferred outcome. A small percentage of post-Carpenter cases involve courts applying a strong version of a doctrine that Carpenter curtailed. These opinions may represent a small pocket of indirect resistance towards Carpenter. Yet judicial inertia towards a prior status quo is a common phenomenon following a major legal change, and its occurrence here is not too surprising. Judges confronting an unfamiliar new standard that raises decision costs and increases uncertainty are likely to favor the prior doctrine—at least until they grow more comfortable with the new one.  This effect has been observed in areas including criminal sentencing, patent remedies, copyright fair use, qualified immunity law, and many more.

The article also assesses how state courts apply federal constitutional law, blending federal and state interests in unique ways. Here, as in some other situations, state courts appear to be more amenable to broad assertions of federal constitutional rights than federal courts are. Surprisingly, this has nothing to do with political affiliation – party of the appointing president had no correlation with outcomes in these Fourth Amendment cases. It may have more to do with state judges' relative lack of experience with the prior doctrine and greater openness to the new one.

Finally, the article analyzes the enormous practical impact of the “good faith exception” to the exclusionary rule, which permits the government to use unconstitutionally obtained evidence to convict defendants if such evidence was collected in reliance on prior law. Over a third of all substantive post-Carpenter cases in the dataset were resolved on the basis of the good faith exception. The article describes how this exception gives the police powerful incentives to push the envelope on aggressive new surveillance technologies before courts can rule them unconstitutional.