The presidential election of 2004 was scheduled for Tuesday, November 2. The two candidates were incumbent president George W. Bush, Republican of Texas, and U.S. Senator John F. Kerry, Democrat from Massachusetts. Ralph Nader, former Green Party nominee (2000), ran independently in 2004. He stood in the tradition of winless third-party candidates who have nevertheless influenced the outcome of numerous presidential elections. To win their respective party's nomination, the two main contenders ran in a nationwide series of primaries and caucuses. For the incumbent, the process was a formality. For the challenger, the effort was arduous. A primary is a state-level election in which voters choose a candidate affiliated with a political party to run against a candidate who is affiliated with another political party in the general election in November. A primary may be either open — allowing any registered voter in a state to vote for a candidate to represent a political party, or closed — allowing only registered voters who belong to a particular political party to vote for a candidate from that party. A caucus is an informal meeting with candidates and potential voters in which participants discuss their preference for a certain candidate, and delegates, pledged to a particular candidate, are selected to go to party conventions. In Iowa, one of the six U.S. states to hold a caucus, a candidate must have at least 15 percent of the vote to send delegates on to a county convention. The supporters of candidates who do not receive at least 15 percent of the vote must choose a more viable candidate or none at all. A caucus is the most local form of election politics, with voters being directly involved in the process. Included among the delegates are superdelegates who are elected officials or political party leaders appointed to the party conventions outside the primary and caucus system. Superdelegates may or may not have made a commitment to vote for a candidate. The Republicans don't call them superdelegates, but Republican National Committee members will be automatic delegates at this year's convention. In addition to Senator Kerry, Democrats contending for their party's nomination included Ohio Representative Dennis Kucinich and the Reverend Al Sharpton. Others who ran included retired General Wesley Clark, House Minority Leader Richard Gephart, retiring Florida Senator Bob Graham, Connecticut Senator Joe Lieberman, former Illinois Senator Carol Moseley Braun, former Vermont governor Howard Dean and North Carolina U.S. Senator John Edwards.