The American President is perceived as extremely powerful and also as constrained in a number of ways. This paper considers the actual power of an American President compared with the perceived power. It also compares the role of the American President to that of the British Prime Minister.
From the Paper:
"It is certainly the case that American Presidents are viewed and indeed portrayed as powerful individuals. Part of this is due to the media's focus on the personality of presidents and presidential candidates at the expense of their policies and actual role. A President's influence in Washington relies on how he is perceived by the public - more so than a Prime Minister's, which depends more on the view of his cabinet and parliament, which is then adopted by he media - and so this public image is continuously cultivated by the President himself."