Who is primarily responsible for issuing security clearances?

The Department of Defense is primarily responsible for issuing security clearances. This responsibility stems from its role in national security and the protection of sensitive information related to defense operations. The Department of Defense has established comprehensive processes for evaluating individuals' backgrounds, including their character, loyalty, reliability, and trustworthiness, to determine whether they can be granted access to classified information.

This authority is derived from national security policies and regulations that define who can access classified materials, with the Department of Defense often serving as the leading agency managing these evaluations. The processes involve extensive investigations and reviews, ensuring that only individuals who meet stringent standards of suitability can receive security clearances.

The other departments, while they do handle security-related responsibilities within their domains, do not primarily manage the issuance of security clearances in the same way the Department of Defense does. Therefore, the clear alignment of the Department of Defense's role with the issuance and oversight of security clearances makes it the correct answer.