Final answer:
The Department of State is responsible for making U.S. foreign policy and handling treaty negotiations.
Step-by-step explanation:
The cabinet department responsible for making foreign policy and handling treaty negotiations in the United States is the Department of State. The Department of State is the lead U.S. foreign affairs agency. The Secretary of State serves as the President's principal foreign policy adviser and directs the department in developing and implementing the President's foreign policy. In contrast, other departments such as the Department of Defense and the Department of Homeland Security also play significant roles in foreign policy, with the former focusing on military aspects and the latter on security within U.S. borders.