Article II of the Constitution says the president has the power to:
- make treaties with other countries (with consent of the Senate),
- appoint ambassadors to other countries (with consent of the Senate)
- and receive ambassadors from other countries
Article II also establishes the president as commander-in-chief of the military, which gives him or her a lot of control over how the United States interacts with the world. As Carl von Clausewitz said, "War is the continuation of diplomacy by other means."
Using the Power
The president's authority in all things is exercised through various parts of his or her administration. Therefore, understanding the executive branch's international relations bureaucracy is one key to understanding how foreign policy is made.
Outside the Executive Branch
But the president has plenty of company in steering the ship of state. Congress plays a key oversight role in foreign policy and sometimes plays a direct role as well. As noted above, the Senate's role in approving treaties and U.S. ambassadors is affirmed in the U.S. Constitution.
Increasingly, state and local governments exercise their own kind of foreign policy. Often this takes the form of trade and agricultural interests. But the environment, immigration, and other issues are involved as well.
Some of the most important players in shaping U.S. foreign policy are outside of government. "Think tanks" and non-governmental organizations serve a major role in crafting and critiquing American interactions with the rest of the world. These groups and others - often including former U.S. presidents and other former high ranking officials - have interest in, knowledge of, and impact on global affairs which can span longer time frames than any particular presidential administration.