Replication Data for: Where Have All the Experts Gone? The Shifting Marketplace for Foreign Policy Ideas on Capitol Hill

US foreign policy observers have noted a decline in the frequency of expert witnesses appearing before congressional committees, while congressional scholars have documented changes in committee practices that have led to fewer and shorter hearings. These trends interact in systematic ways, although their relationship has never been tested empirically. Using original data and micro-level measures of individual hearings by the national security committees of the House and Senate, we demonstrate how time constraints and routine responsibilities limit the number of opportunities for expert witnesses from 1995 to 2020. We find some influence for chamber polarization on witness totals but less impact on the type of experts. We uncover significant differences among individual committees in their use of academics and think tank representatives. Our study is unique in its focus on both chambers, inclusion of closed hearings, differentiation between academics and think tank representatives, and attention to the public salience of foreign affairs. Shrinkage in the official marketplace of foreign policy ideas warrants concern, highlighting the executive branch's increasing dominance over military and diplomatic decisions, diminished legislative capacity, and public disinterest in international affairs.