When Americans cast their ballots for President and Vice President they do not directly vote for the candidates of their choice. Instead, voters are actually casting their ballots for “electors” in their state, who then cast votes known as “Electoral Votes." This body of electors nationwide is known collectively as the Electoral College, and it is their votes, and not the nationwide popular vote, that chooses the President and Vice President of the United States.
In keeping with the idea of representative government that the nation was founded upon, the Electoral College was originally designed to be a deliberative body of citizens elected by voters to select the President and Vice President. However it soon evolved into the system we have today, where the voters choose electors who are pledged to a certain candidate.
Each state and the District of Columbia is allotted a number of electoral votes equal to their total Congressional representation. There are 538 members of Congress so there are 538 electoral votes. To win the election the candidates must win a simple majority of the 538 votes, or 270 votes.
Forty-eight states and the District of Columbia have a winner-take-all system, whereby the winner of the state’s popular vote is awarded all of the state’s electoral votes. Two states, Nebraska and Maine, use a proportional system, where the electoral votes of the state are awarded by the percentage of the popular vote received.
Because the winner is determined by the electoral vote and not the national popular vote, it is possible to receive more popular votes but less electoral votes, and therefore lose the election. While this situation isn't common, it happened most recently in 2000 when Al Gore received more popular votes but lost to George W. Bush, who received a majority of the electoral votes.
The controversy surrounding the 2000 election led to a renewed interest in abolishing the electoral college system and establishing the nationwide popular vote as the method of electing the President and Vice President. Opponents of the electoral college believe it to be archaic and feel that a nationwide popular vote would be the fairest way to select the President and Vice President, as every vote cast would count towards a candidate's total.
Proponents of the electoral college say that because the current system is really the result of 51 separate elections in the individual states and the District of Columbia as opposed to one national election, it encourages candidates to visit states throughout the nation, as opposed to concentrating their efforts solely on those with large populations. Supporters also say that the electoral college can create a greater sense of a "mandate" for the winning candidate, as the percentage of victory in electoral votes is often times greater than in the nationwide popular vote.
One example of this is the 2008 election, where Barack Obama received 53% of the popular vote yet he received 68% of the electoral vote, creating the sense that he won in a landslide, although he and John McCain were separated by only 8 million votes out of the approximately 125 million votes cast.