The major political groups in Missouri are the Democratic Party and the Republican Party, each affiliated with the national party organization. Before 1825, the state had no organized political parties, and candidates ran as independents; however, each of Missouri's first four governors called himself a Jeffersonian Republican, allying himself with the national group from which the modern Democratic Party traces its origins. Except for the Civil War and Reconstruction periods, the Democratic Party held the governorship from the late 1820s to the early 1900s. Ten Democrats and seven Republicans served in the statehouse from 1908 through 1985. The outstanding figures of 20th century Missouri politics were both Democrats: Thomas Pendergast, the Kansas City machine boss whose commitment to construction projects bore no small relation to his involvement with a concrete manufacturing firm, and Harry S. Truman, who began his political career as a Jackson County judge in the Kansas City area and in 1945 became 33rd president of the United States.
After voting consistently for Republican presidential candidates in the 1980s, Missouri was carried by Democrat Bill Clinton in 1996. In the 2000 presidential election, Missourians once again voted Republican, with George W. Bush receiving 51% of the vote to Democrat Al Gore's 47%. Green Party candidate Ralph Nader won 2% of the vote. In 2002 there were 3,681,844 registered voters; there is no party registration in the state. The state had 11 electoral votes in the 2000 presidential election.
Democrat Mel Carnahan was reelected to the governorship in 1996. In October 2000, Carnahan was running for the US Senate against Republican John Ashcroft when he died in a plane crash with his son and a political aide. Carnahan was elected posthumously to the Senate in November, and his wife Jean accepted an appointment to his seat. She served until 2002, when she was defeated by former US Representative and Republican Jim Talent in an extremely close race. As of 2003, Missouri's US senators were both Republicans—Talent, and Christopher Bond, reelected in 1998. In 2000, Democrat Bob Holden was elected governor. Following the 2002 elections, four of the state's US representatives were Democrats; five were Republicans. In the state senate in mid-2003, there were 14 Democrats and 20 Republicans; in the state house, there were 73 Democrats and 90 Republicans.