(Reuters) - The Electoral College was established in the Constitution as a compromise between electing a president by a vote in Congress and by popular vote of citizens. Here are some facts about the Electoral College:
* The Electoral College, which is not a place but a process, consists of 538 electors. To win the presidency, a candidate must win at least 270 electors.
* The number of electors equals the number of lawmakers in Congress - 435 in the House of Representatives and 100 in the Senate, plus three for the District of Columbia. Each state’s allotment of electors equals its number of representatives in the House plus one for each of its two senators.
* Most states have a winner-take-all system for awarding electors. The presidential candidate who wins the popular vote in the state gets all of the state’s electors. Maine and Nebraska have a variation of “proportional representation” that can result in a split of their electors between the candidates.
* Critics say the Electoral College does not meet the original intent because a candidate can lose the nationwide popular vote and still win the election by winning the right combination of states. That happened most recently in the controversial election of 2000 when Democrat Al Gore got the most votes but Republican George W. Bush won the presidency. Republicans Rutherford B. Hayes in 1876 and Benjamin Harrison in 1888 also won in the Electoral College despite losing the popular vote.
* There is no constitutional requirement that electors vote according to the results of the popular vote, although some states require it.
* The electors meet in their states in December and cast their votes for president and vice president.
* If no presidential candidate reaches 270 electoral votes, the election goes to the House of Representatives, with each state having one vote.
The House has decided two presidential elections - that of Thomas Jefferson in 1800 and John Quincy Adams in 1824.
The Senate would elect the vice president, with each senator casting one vote. That raises the possibility of a president and vice president from different parties.
* The biggest Electoral College prizes are California, with 55; Texas, with 38; and New York and Florida, each with 29. California and New York are considered reliably Democratic, Texas reliably Republican and Florida is a battleground state that could go either way.
* Among the other important swing states this year, Ohio has 18 votes, Virginia 13, Wisconsin 10, Colorado 9, Nevada 6, Iowa 6 and New Hampshire 4.
* The system explains why candidates tend to spend a disproportionate amount of time and money on trying to secure the battleground states. It also means that what appears to be a tight race in national opinion polls may be less close when viewed state by state.
SOURCES: U.S. National Archives and Records Administration, Reuters.
Editing by Jim Loney and Peter Cooney