WASHINGTON (Agencies) - Most American voters are expected to cast their ballots on Nov 4 (today) to choose the next president between Democratic candidate Barack Obama and Republican hopeful John McCain, and draw to an end the nearly year-long election campaign in 2008. Starting in 1792, US presidents and vice presidents have been elected quadrennially on election day, the first Tuesday after the first Monday of November. As a matter of fact, voters only cast their ballots for a slate of electors of the US Electoral College, who in turn directly elect the president and vice president. The current US presidential election system, featuring the electoral college, was originally established by Article Two of the Constitution, as a result of a compromise between those who wanted Congress to choose the president, and those who preferred a national popular vote. The whole process of the presidential election features four phases, namely the primary elections, nominating conventions, the presidential nominee campaign and the national popular vote. During the nomination race, usually from January to June, primaries and caucuses are held in 50 states, the District of Columbia and all US territories to elect a presidential nominee for each major political party. After winning the primary elections, each party's presidential nominee chooses a vice presidential nominee to run with him or her. The pair receive their official nominations at their party's national conventions, which take place during the summer of election year. Between the conventions and election day, all parties' presidential candidates run their campaign nationally, holding rallies, broadcasting TV ads and giving interviews. They have to repeatedly adjust and state their policies and stances toward all issues concerning voters at home and abroad, and face challenges from rivals. As millions of US dollars are needed for the longtime and extensive presidential campaign, candidates have to exert themselves to collect political donations from the public and their parties throughout election year. On election day, voters, generally, are required to vote on a ballot where they select the candidate of their choice, but the ballot is actually voting to select the electors of a candidate. Under the Constitution, each state is allocated a number of Electoral College electors equal to the number of its Senators and House Representatives in the US Congress. The District of Columbia is given three electors, the same amount held by the smallest state. No representative of the US territories is in the body. The formal process to elect the president will not take place today. After Americans cast their votes for their choice of president and vice president by voting for correspondingly-pledged electors, they then have to wait for the Electoral College to meet and formally elect the president on December 15. Most states, excluding Maine and Nebraska, employ the "winner-takes-all" system, meaning whichever ticket wins a plurality of voters in a certain state wins all of the state's electoral votes. Any pair of presidential and vice presidential candidates who gain at least 270 electoral votes of the total 538 are claimed the winners. Although the president and vice president-elect can be yielded on election day, the official voting for them by the Electoral College is held on the first Monday after the second Wednesday in December. If no presidential candidate wins at least 270 electoral votes, the selection is decided by the House of Representatives. If no vice presidential candidate receives a majority, the decision is left up to the Senate. The new president and vice president are supposed to be sworn in on Jan. 20. In case the House of Representatives has not chosen a president-elect by that date, the vice president-elect becomes the acting president until the floor makes the decision. If the vice president-elect is also not known by then, the sitting House Speaker becomes the acting president. Election day also witnesses the re-election of all House Representatives and one third of Senators as well as some governors and local government officials. In addition to candidates from the Democratic and Republican parties, several third parties also put their candidates' names on the tickets. However, mainly due to the "winner-takes-all" method of states awarding electoral votes, US electoral politics is still dominated by the two major parties. Another peculiarity of the US system is that eastern seaboard states such as New York and Maine finish voting five hours before California and even further ahead of Hawaii. Thus, the voters of the Pacific coastal areas know the results back east before they turn out to vote. Once America has voted, the president-elect doesn't wait for Electoral College confirmation. He will prepare his administration and appoint officials and ambassadors as he gets ready to take control of the Oval Office after being sworn in, traditionally by the Chief Justice, at the inauguration ceremony on January 20. His address that day is a key event in US politics, where the president sets out a vision and tone for the first four years of his administration.