The president's power is limited by a system of checks and balances written into the United States Constitution. The legislative and judicial branches have specific power to deny or impede the executive branch's actions.
The system of checks and balances was added to the Constitution so that no one branch of government would grow too powerful. The framers of the Constitution saw the complete power that the British monarch had over his country and designed American government to prevent this situation from reoccurring.
The legislative branch can override presidential vetoes with a two-thirds vote. Since the legislative branch is responsible for budgeting, it can limit the president's actions by stopping the flow of resources. Additionally, the legislative branch can impeach the president for wrongdoing with a two-thirds vote. The president must also have approval from Congress before enacting treaties with or declaring war on foreign nations. Although the president has the power to appoint Supreme Court judges, the appointments must be approved by Congress.
In the judicial branch, judges cannot be removed by the president once installed. The courts also have the power of judicial review, which examines actions from the other branches for constitutionality. If an executive action is called into question, the Supreme Court can annul it.