Despite a number of compelling entrapment claims in post-9/11 US terrorism cases, these claims have nearly always failed. While previous research suggests possible reasons for this almost complete failure of the entrapment defense, no research has yet systematically examined the mechanisms responsible for this result. Drawing on thirty-seven interviews with individuals with in-depth knowledge of particular cases, as well as textual analysis of court decisions and quantitative analysis of a terrorism database, this article identifies several factors contributing to the entrapment defense’s failure. These include strategic choices by defendants to plead guilty or use other defenses, prosecutorial misconduct, evidence manipulation by informants and police, deficient entrapment doctrines, and procedural irregularities. Consistent with the general trend of counterterrorism law enhancing government power while reducing accountability, the multiple opportunities for authorities to manipulate the legal process leave defendants with little realistic chance of acquittal on entrapment grounds.