Washington: The long and hard-fought battle for the White House between President Barack Obama and Republican challenger Mitt Romney would create history - whichever way it ends on Election Day Nov 6.
If Romney, who is narrowly ahead on average in national polls, wins, he would become the fourth challenger to oust a sitting president since World War II and the first Mormon to occupy the White House.
Before him Democrat Jimmy Carter did so defeating Gerald Ford in 1976, Republican Ronald Reagan turned the tables on Carter in 1980 and Democrat Bill Clinton ousted Reagan's successor, George H.W. Bush, in 1992 due to a struggling economy.
If Obama, who created history four years ago to become the first African American president, retains the world's most powerful job, he would be one of the rare presidents to win despite "It's the economy, stupid" as a Clinton campaign strategist summed it up in 1992.
But before the Obama-Romney face-off began, the two had to come through what are called the primaries where voters, registered as Democrats or Republicans and independents, choose 'electors' in each state to pick up their party's candidate.
In most states only registered voters of a particular party can vote in its election, but some others have open primaries where anyone can vote irrespective of party affiliation. But unlike in India, party bosses have no role in the selection process.
Romney officially threw his hat into the ring as early as April 2011. But it was only on Aug 28 this year that battling many a party stalwart through ups and downs in primaries and caucuses, where only a limited number of party functionaries vote, he was anointed the party's flag bearer.
For Obama, as an incumbent president running for re-election, the race for the Democratic nomination was largely uneventful. But he too had to go through the nomination process of primaries and caucuses in all the 50 states before he won the right to carry the Democratic flag.
Then on to the battle main the contenders go through a similar process. But unlike the primaries all states go to the polls on the same day - always the Tuesday after the first Monday in a leap year.
Contrary to popular perception, people would not be directly voting for Obama or Romney or their running mates, but would only be picking up largely unnamed "Electors for Barack Obama and Joseph Biden," or "Electors for George Romney and Paul Ryan".
Each state picks 'electors' equal to the combined total of its Senate - two for each state irrespective of the size - and House members allocated on the basis of its population, to form what is called the Electoral College.
Thus California, America's most populous state, has 55 electoral votes, while a number of states like Alaska, Delaware, Montana, Vermont, Wyoming and the Dakotas have just three votes each. The winner takes all of a state's electoral votes.
Devised by the founding fathers as a compromise between America's federal structure giving primacy to the states and the exercise of popular will, it's the Electoral College that chooses the president and vice president by majority vote.
The 538 electors so chosen will meet in the state capitals Dec 17. They are duty bound to vote for the winning candidate in their state irrespective of their own party affiliation, but there have been nine 'faithless' electors since 1900, who have voted against the candidates to whom they were pledged.
Then the Congress meets in a joint session Jan 6, or Jan 7 this year as Jan 6 happens to be a Sunday to count the electoral votes and declare the winning pair that takes office on Jan 20 - one who reaches the magic number of 270 and not the one who polls more votes Nov 6.