The third factor is that Obama has an electoral-college advantage and a decided organizational edge.
Pennsylvania, with its 20 electoral-college votes, was one of the first crucial states to be called for Obama.
And so, Bill Clinton won an electoral-college landslide, with just 43 percent of the popular vote.
The presidential electors who meet after the citizens vote for president and cast ballots for the president and vice president. Each state is granted the same number of electors as it has senators (see United States Senate) and representatives combined. These electors, rather than the public, actually elect the president and the vice president. The Founding Fathers assumed that electors would exercise discretion and not necessarily be bound by the popular vote, but the rise of political parties undermined this assumption. Electors are now pledged in advance to vote for the candidate of their party, and nearly always do so. Thus, the vote of the Electoral College is largely a formality.
Note: There have been several attempts to abolish the Electoral College. In the 2000 presidential election, the candidate with the plurality of popular votes lost the electoral vote, a situation that also occurred in the 1876 and 1888 elections.