President of the United States(7)

Duties and powers
Main article: Powers of the President of the United States
The president is the chief executive of the United States, putting him at the head of the executive branch of the government, whose responsibility is to "take care that the laws be faithfully executed". To carry out this duty, he is given control of the four million employees of the vast executive branch, including one million active duty personnel in the military. Both the legislative and judicial branches maintain checks and balances on the powers of the president, and vice versa.
Various executive and judicial branch appointments are made by presidents, including presidents-elect. Up to 6,000 appointments may be made by an incoming president before he takes office, and 8,000 more may be made while in office. Ambassadors, judges of the federal court system, members of the Cabinet, and other federal officers are all appointed by the president, with the "advice and consent" the Senate, granted by a simple majority. Appointments made while the Senate is in recess are temporary and expire at the end of the next session of the Senate. He may also grant pardons, as is often done just before the end of a presidential term.
In addition, while the president cannot directly introduce legislation, he can play an important role in shaping it, especially if the president's political party has a majority in one or both houses of Congress. While members of the executive branch are prohibited from simultaneously holding seats in Congress, they often write legislation and allow a member of Congress to introduce it for them. The president can further influence the legislative branch through the annual constitutionally-mandated report to Congress, which may be written or oral but in modern times is the State of the Union Address, which often outlines the president's legislative proposals for the coming year. If Congress passes a bill that the president disapproves of, he may veto it; the veto can be overridden only by two-thirds of both houses of Congress, making it substantially more difficult to enact the law.
Perhaps the most important of all presidential powers is command of the armed forces as commander-in-chief. The framers of the Constitution took care to limit the president's powers regarding the military; Federalist No. 69 states in part:
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The President is to be commander-in-chief of the army and navy of the United States. [...] It would amount to nothing more than the supreme command and direction of the military and naval forces [...] while that [the power] of the British king extends to the DECLARING of war and to the RAISING and REGULATING of fleets and armies, all [of] which [...] would appertain to the legislature.[7]
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While the power to declare war is constitutionally vested in Congress, the president commands and directs the military and is responsible for planning military strategy. Congress, pursuant the War Powers Act, must authorize any troop deployments more than 60 days in length. Military spending and regulations are also governed by Congress, providing a check to presidential power. Along with the armed forces, foreign policy is also directed by the president, including the ability to negotiate treaties, which are ratified with the consent by two-thirds of the Senate.
Source : http://en.wikipedia.org/wiki/President_of_the_United_States