Constitutionally mandated process for electing the U.S. president and vice president. Each state appoints as many electors as it has senators and representatives in Congress (U.S. senators, representatives, and government officers are ineligible); the District of Columbia has three votes. A winner-take-all rule operates in every state except Maine and Nebraska. Three presidents have been elected by means of an electoral college victory while losing the national popular vote (Rutherford B. Hayes in 1877, Benjamin Harrison in 1888, and George W. Bush in 2000). Though pledged to vote for their state's winners, electors are not constitutionally obliged to do so. A candidate must win 270 of the 538 votes to win the election.