Chile's government is a representative democratic republic, whereby the President of Chile is both head of state and head of government, and of a formal multi-party system that in practice behaves like a two-party one, due to binomialism. Executive power is exercised by the government. Legislative power is vested in both the government and the two chambers of the National Congress. The judiciary is independent of the executive and the legislature of Chile. The Constitution of Chile was approved in a national plebiscite in September 1980, under the military government of dictator Augusto Pinochet. It entered into force in March 1981. After Pinochet left power in 1988, saying this country was ready to keep going along with a plebiscite, the Constitution was amended to ease provisions for future amendments to the Constitution. In September 2005, President Ricardo Lagos signed into law several constitutional amendments passed by Congress. These include eliminating the positions of appointed senators and senators for life, granting the President authority to remove the commanders-in-chief of the armed forces, and reducing the presidential term from six to four years while also disabling immediate re-election.