The U.S. Transportation Security Administration (TSA) is collaborating with a team of system dynamics modelers from the national laboratories to build a model of their security checkpoint operations at US commercial airports for the purpose of proactively identifying high-leverage opportunities for investment to improve system performance. To elicit a broad range of expertise and opinions to develop our understanding of the systemic issues facing TSA as they strive to improve their security checkpoint operations, we conducted more than 30 interviews with headquarters and field-operations staff and hosted a 2-day group model building exercise. In this paper, we use both causal-loop diagrams together with a description of the results of the group model building exercise to present a rich articulation of the issues facing TSA in managing their security checkpoints. We also show how the complex interrelationships among various factors ultimately impact the effectiveness and efficiency of the aviation security checkpoint.