In the United States, the Constitution and the system of checks and balances are designed to prevent a President from becoming an all-powerful dictator. The Constitution divides the powers of the federal government among three branches: the legislative, executive, and judicial. The President is the head of the executive branch, but he or she is subject to checks and balances from the other two branches.
The legislative branch, composed of the House of Representatives and the Senate, has the power to pass laws and approve presidential appointments. The President cannot make laws or appointments without the approval of Congress.
The judicial branch, composed of the Supreme Court and other federal courts, has the power to interpret the Constitution and determine the constitutionality of laws and actions taken by the President. If the President were to violate the Constitution, the courts could declare his or her actions unconstitutional and stop them.
In addition to these checks and balances, the President is also subject to the rule of law and the oversight of the media, interest groups, and the public. If the President were to abuse his or her power or violate the Constitution, these forces could mobilize to hold the President accountable.
Finally, the President is subject to term limits. A President can serve no more than two four-year terms, after which he or she must step down. This ensures that no single individual can hold the office of President for an extended period and accumulate too much power.