This article examines the role of former National Security Adviser H. R. McMaster in the Trump administration. The article discusses four major roles performed by the APNSA - administrator, coordinator, counselor, agent - and asserts that McMaster served as a coordinator that failed to achieve a close relationship with the president. Probing the role and performance of President Trump's second APNSA underscores both the significance of a partly influential APNSA and apparent constraints in relation to what a president with a unconventional management style allowed him to do. Examining the importance of presidential management style on the role, power and influence of the APNSA will further our understanding of how, when, and under what conditions national security-level leaders make decisions.