The President of the United States has many fundamental powers, some are granted to him by the Constitution while others are not. The President is commander in chief of the armed forces and National Guard when they are called into federal service. The President appoints, with the consent of the Senate, heads of executive departments. The chief executive may pardon people convicted of federal crimes, except in cases of impeachment, or reduce a person's jail sentence or fine. The President makes treaties with the advice and consent of Senate, and appoints ambassadors, federal court judges, justices of the Supreme Court, and other top officials, with Senate consent. The chief executive delivers an annual State of the Union message to Congress and sends other special messages to Congress from time to time. The President calls Congress into session when necessary, and meets with heads of states, ambassadors, and other public officials of foreign countries. The President commissions all military officers of the United States, and ensures that the laws Congress passes are "faithfully executed." Although the Constitution grants specific powers to the President, other sources of presidential power include the actions of past Presidents, grants of power from Congress, and the President's use of the mass media. .
The Founders also built safeguards against the abuse of presidential power into the Constitution. Both Congress and the courts have powers that limit the President's authority. Other factors, not mentioned in the Constitution, also affect the President's actions. Congress has the power to pass legislation over a President's veto, which limits the President's effectiveness in carrying out legislative program or in using executive powers. Congress also has the power to impeach a President. The federal courts have a constitutional power to limit a President, however, they are inclined to respect President's views and authority.