The United States Constitution divides the federal government into three branches so that no person or group would have too much power. These are Legislatative, Executive Body and Judicial. Each branch of government can change the acts of other branches. The president can veto legislation created by Congress and appoint heads of federal agencies. The Congress may confirm or dismiss the President's candidates and can remove President from office in certain circumstances. Judges of the Supreme Court may abolish unconstitutional laws, suggested by President, and the senate confirms them.
In addition, the executive has the authority to check the work of the legislature, putting a veto on the laws Congress wishes to implement. Legislative branch can check executive branch by passing laws over the veto by two-thirds vote in each house. The judicial branch can check both the legislative and executive branches by declaring the law unconstitutional.