Final answer:
Agency is a relationship where the agent acts on behalf of the principal. The highest form of political power is legitimacy. In foreign policy, the president shares power with Congress.
Step-by-step explanation:
The question discusses a relationship in which one person is authorized by another to act on their behalf in dealing with third parties. The correct answer to fill in the blanks is A) Agency; Principal; Agent. An agency is a relationship where the agent is authorized by the principal to represent them in interactions with third parties. The highest form of political power is not an individual like the president or a specific entity like the Supreme Court; rather, it is the concept of legitimacy, which refers to power that people recognize and accept as right. When discussing formal powers, especially in the realm of foreign policy, it's important to note that while the president has significant authority, this power is often shared with Congress. This demonstrates a balance of power and a system of checks and balances that are a cornerstone of the United States government framework.