By Professor Larry Sabato
University of Virginia
The odds are that the victor of the American presidential election on 4 November will secure a clean-cut victory in the electoral college - an absolute majority of 270 votes or more.
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The closer the election gets - and right now the polls have it very tight indeed - the greater the chance that a tie of 269 to 269 will occur.
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Given the results in 2000 and 2004, when Michigan and Pennsylvania voted Democratic, it is not unreasonable to assign them to Obama, bringing him to 260, just 10 votes short of the White House. While Obama has a real chance to win in Colorado, Ohio, and Virginia, all three states have tended to vote Republican in many or most election years.
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If you mix and match states on the map, in fact, you will quickly see that it relatively easy to produce a tie in the electoral college. So what happens if one occurs? In two words: a mess.
Under the constitution, the election for president is thrown into the US House of Representatives, while the Senate picks the next vice-president (the Senate's presiding officer).
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more:
http://news.bbc.co.uk/2/hi/americas/7626471.stm