The politics of Mexico function within a framework of a federal presidential representative democratic republic whose government is based on a multi-party congressional system , where the President of Mexico is both head of state and head of government. The federal government represents the United Mexican States and is divided into three branches: executive, legislative and judicial, as established by the Political Constitution of the United Mexican States, published in 1917. The constituent states of the federation must also have a republican form of government based on a congressional system as established by their respective constitutions.
The executive power is exercised by the executive branch, which is headed by the President, advised by a cabinet of secretaries that are independent of the legislature. Legislative power is vested upon the Congress of the Union, a two-chamber legislature comprising the Senate of the Republic and the Chamber of Deputies. Judicial power is exercised by the judiciary, consisting of the Supreme Court of Justice of the Nation, the Council of the Federal Judiciary and the collegiate, unitary and district tribunals.
The politics of Mexico are dominated by four political parties: Institutional Revolutionary Party (PRI), National Action Party (PAN), Democratic Revolution Party (PRD), and the National Regeneration Movement (MORENA). Founded in 1929 as the Partido Nacional Revolucionario ("National Revolutionary Party"), PRI has dominated Mexican politics for over 70 years bringing to power 11 different governments. PAN was founded in 1939, but it did not win its first governorship until 1989; its candidates won the presidency in 2000 and 2006. The beginnings of PRD go back to 1988 when dissident members of PRI decided to challenge the leadership and nominated Cuauhtémoc Cárdenas for president of Mexico. Cardenas lost in a highly contested election, but a new political party was born and the party emerged as a third force in Mexican politics, even though they have never captured the presidency.