The Framers were hesitant on giving much power to the President, they were afraid of possible tyranny and because of that the powers of the President were not very much listed. The first three presidents (Washington, Adams, and Jefferson) were the ones that established the importance of the Presidency. Washington helped to establish the President's powers and Jefferson used the party system to expand the role of the president in the legislative process.
At the same time, the Checks and Balances system was able to limit some of the Presidents powers, the Legislative Branch can limit the presidential power by refusing to accept one of the president's appointees. The Judicial Branch can consider any Presidential act unconstitutional. For example, the US Supreme Court in the case Hamdan v. Rumsfeld rejected George W. Bush’s use of military commissions without congressional approval.