Although there has been a voluminous literature on American foreign policy and its effect on several regions, research on American domestic politics has been relatively scarce. Due to its significant impact on foreign policy formation, the Presidency received a lot of scholarly attention. This paper, on the other hand, focuses on another important actor in American foreign and domestic policy: The United States Congress. In this respect, we specifically aim to contribute to the literature on American Congress which aims to uncover the party effect on legislative behavior. Current studies on the topic usually rely on roll-call votes. Although this method has been quite popular, recent studies indicate problems in terms of measuring the true effect of the party. Hence, this study proposes an alternative method which has been widely used in the European Politics literature. The proposed methods involves using expert surveys to determine the level of party effect.