Which of the following is a Cabinet-level position?

The position of Secretary of Defense is a Cabinet-level role because it is part of the President's Cabinet, which comprises the heads of the executive departments. The Cabinet is a group of advisors who help the President make decisions on important national issues and implement laws. The Secretary of Defense specifically is responsible for overseeing the nation's military and defense policies, playing a crucial role in national security.

In contrast, an ambassador represents the U.S. in foreign countries but does not hold a Cabinet position. Senators are part of the legislative branch of government and do not serve in the President's Cabinet. Federal judges oversee court cases but are part of the judicial branch, independent of the executive branch where Cabinet positions are found. This distinction underscores the role of the Secretary of Defense as a part of the executive team that directly advises the President.