Synder and Groseclose (2000) develop and apply an innovative method for detecting and estimating the frequency and magnitude of party influence in congressional roll call voting. This paper presents a framework for assessing to coefficient that the authors interpret as “party influence.” The analysis reveals that, and shows why, the coefficient manifests two troublesome characteristics. The coefficient cannot discriminate between disparate types of party influence because the mapping between a types of partisan influence and signs of the coefficient is not one-to-one. Similarity, the coefficient has a responsiveness problem in that a marginal increase in one party’s influence can cause the estimate of the coefficient to increase, decrease, or remain constant. Because the literature on parties in Congress emphasizes majority-constant. Because the literature on parties in Congress emphasizes majority-party strength, the inability of the coefficient to isolate party-specific effects is a serious drawback in the ongoing hunt for genuine party discipline.