Argentina is composed of 23 provinces and one federal district (Buenos Aires). It is governed by the 1853 constitution as revised in 1898 and 1994, and has a federal system of government. The president and vice president are elected by popular vote for four-year terms and can be reelected once. The popularly elected bicameral national congress is composed of 72 senators (three from each province and the federal district), who serve six-year terms, and 257 deputies (based on proportional representation), who serve four-year terms. There is a nine-member supreme court. Each province has its own elected governor and legislature and its own judicial system.