http://wiki.answers.com/Q/What_is_the_role_of_the_presidency

The president has many many many powers.  He can control anything as a commander in chief of the armed forces to enforcing that laws are carried out.  He/She can can also grant reprieves and pardons for federal offenses.

http://en.wikipedia.org/wiki/President_of_the_United_States

The President is the head of state and the head of government of the United States and is responsible for dictating the legislative agenda for his party.

http://www.c-spanclassroom.org/pdf/ws_rolesofthepresident.pdf

The President of the United States is the Party Leader, the Commander-in-Chief of the Armed forces, and the Chief Executive.