Under Articles I and II of the United States Constitution. The President:
* Has the power to approve or veto bills and resolutions passed by Congress
* Through the Treasury Department, has the power to write checks pursuant to appropriation laws.
* Pursuant to the Oath of Office, will preserve, protect, and defend the Consitution of the United States.
* Serves as Commander-in-Chief of the United States military, and militia when called to service.
* Is authorized to require principle officers of executive departments to provide written opinions upon the duties of their offices
* Has the power to grant reprieves and pardons for offenses against the United States, except in the cases of inpeachment.
* Has the power to make treaties, with the advise and consent of Congress.
* Has the power to nominate ambassadors and other officials with the advise and consent of Congress.
* Has the power to fill vacancies that happen when the Senate is in recess that will expire at the end of the Senate's next session.
* Shall periodically advise Congress on the state of the union and give Congress recommendations that are thought necessary and expedient.
* Has the power to convene one or both houses of Cogress during extraordinary occasions, and when Congress cannot agree to adjourn has the power to adjourn them when he thinks the time is proper.
* Has the duty to receive ambassadors and other public ministers.
* Has the duty to see that the laws are faithfully executed.
* Has the power to commission the officers of the United States.
A transcript of the United States Consitution can be found on the National Archives website HERE.