Americans sometimes forget that the U.S. presidential election is not one election, but many. Not only do voters elect delegates to nominating conventions on a state-by-state basis, but the election to the presidency occurs through the Electoral College---chosen on a state-by-state basis rather than by a majority of the popular vote. Politicians need to win what political scientists call the "pivotal" voter in order to be elected to office. In two-party majoritarian elections with a voters distributed along a regular "left-right" continuum, politicians must win the vote of the median voter. So their policy positions will tend to cluster around the policy preferences of the middle voter.