Building on strategic models and the collegial nature of the U.S. courts of appeals, this article assesses the influence of a circuits' composition on individual judges' behaviors and the president's role in shaping the courts. As partisanship is one of the few signals of a nominee's ideology known to an executive administration at the time of appointment, it is important to measure partisan composition as a factor in individual behavior as well as other measures of overall ideology of the circuit. This article finds that the composition of the circuits influences individual behavior, even after controlling for individual ideology, panel effects, and other contextual factors. This remains true whether we examine composition based on partisanship or on more nuanced ideological measures. Noting that presidents, on average, create new partisan majorities within two circuits per four-year term, these findings suggest turnover on circuit courts may have influences on case outcomes outside of a particular new appointee's voting record.