The correct answer is d) broad and vague.
Presidential power has grown primarily due to the fact that their powers outlined in Article 2 of the U.S. Constitution are broad and vague.
The United States Constitution states the powers of the President but in general definitions. This ambiguity has allowed the presidential power to grow during the past years. Among the powers that the Constitution states are that the United States President in the Commander in Chief, is the Chief Executive of the nation, and the Chief Diplomat. But the President also has many informal powers such as issuing executive orders or negotiating executive agreements.