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.美国外交政策领域的观察者注意到，在国会委员会前作证的专家证人的频次有所下降；而国会研究学者则记录了委员会运作模式的变革，这些变革使得听证会的数量更少、时长更短。尽管二者的关联尚未经过实证检验，但这些趋势以系统性的方式相互影响。本研究利用1995年至2020年间美国众议院与参议院国家安全委员会各场听证会的原始数据及微观层面测度指标，阐释了时间约束与常规履职职责如何限制了专家证人的作证机会。研究发现，两院极化现象对专家证人的总人数存在一定影响，但对专家类型的影响相对有限。我们还发现，各委员会在聘请学者与智库代表方面存在显著差异。本研究的独特之处在于：同时聚焦参众两院、纳入闭门听证会、区分学者与智库代表两类证人，并关注外交事务的公众关注度。官方外交政策思想市场的收缩值得警惕，这凸显出行政部门对军事与外交决策的主导性日益增强、立法能力有所弱化，以及公众对国际事务的兴趣减退。