Which of the following is NOT a core mission of the Department of Homeland Security?

The core missions of the Department of Homeland Security (DHS) focus on safeguarding the nation from various threats and ensuring the safety and security of its citizens. Among these missions, border security, immigration policy enforcement, and disaster response are essential components. Border security is vital in controlling and managing the flow of people and goods across the country's borders, while immigration policy enforcement involves upholding and implementing laws that govern the entry and stay of individuals in the country. Disaster response is crucial for managing and mitigating the impacts of natural disasters and emergencies, ensuring communities can recover effectively.

In contrast, foreign policy development is not a core mission of DHS. Instead, foreign policy is primarily the responsibility of the Department of State. DHS may engage in certain international collaborations related to security, but it does not develop foreign policy itself. Therefore, this distinction highlights why foreign policy development is the correct answer, as it falls outside the purview of DHS's primary objectives.