Answer: Foreign policy
Explanation: The power of the presidency has grown exponentially in the area of foreign policy than it was initially. The major explaining variable for that being historical precedence. Now, we have examples of Presidents conducting foreign policy without Congressional approval. A case in point was Harry Truman's decision to fight in Korea without Congress declaration of war.
The U.S. presidents by the early 1960s had become the sole architect of U.S. foreign policy.
