As part of the system of checks and balances, in which all branches of the government can respond to the action of the other, the Judicial Branch has the power to Judicial Review: its power to influence the other branches.
Judicial review is the Supreme Court's right and power to review laws (in the local, state and federal level) and acts of the executive and legislative branches and determine their constitutionality.
For example, if the President ever decides to declare war on a country and spread it to the media. The Judicial branch is the one that can formally denounce that their actions are unconstitutional since it is the Legislative Branch, and not the President, the one that can declare war. And if Congress passes a law that is against the Constitution, such as a law that established that the government can acquire private property for whatever reason, the Judicial Branch is the one able to determine the law unconstitutional based on the Fifth Amendment that protects the right to private property.
