Nigeria is a federal republic modeled after the United States, with executive power exercised by the president. The government of Nigeria is also influenced by the Westminster System model in the composition and management of the upper and lower houses of a bicameral legislature. The president, however, is the head of state, the head of government, and the head of a multi-party system. Nigerian politics takes place within a framework of a federal, presidential, representative democratic republic, in which executive power is exercised by the government. Legislative power is held by the real government and the two chambers of the legislature: the House of Representatives and the Senate. Together, the two chambers make up the law-making body in Nigeria, called the National Assembly, which serves as a check on the executive arm of government. The highest judiciary arm of government in Nigeria is the Supreme Court of Nigeria. Nigeria also practices Baron de Montesquieu's theory of the separation of powers based on the United States system.