Who serves as the principal assistant to the President regarding matters related to the Department of Defense?

The principal assistant to the President concerning matters related to the Department of Defense is the Secretary of Defense. This role encompasses a wide range of responsibilities, including formulating defense policy, overseeing military operations, and managing the Department of Defense's budget. The Secretary serves as the main conduit for information and recommendations on defense issues, and is the highest-ranking military official in the cabinet, ensuring that military strategy aligns with national interests. This position directly interacts with both military leaders and civilian policymakers to ensure a cohesive defense policy, as well as to advise the President on military issues and decisions. The Secretary of Defense plays a crucial part in coordinating between the armed forces and the White House, which is vital for national security and defense matters.