Acting under which title does the President have overall responsibility for all interactions between the United States and foreign countries?

The title of the President that gives him responsibility overall for foreign interactions is the Chief of State.

Explanation:

The President represents the United States to the rest of the countries and governments around the world. Thus the President is in charge of advancing the values and ideals of the United States and protecting the interests of the United States on the global stage. The President is the maximum authority representing our foreign interests abroad.  The President represents the United States in global alliances like the G8 and he meets bilaterally with other world leaders to negotiate treaties and agreements that promote trade and investment that is beneficial for the country.

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