The US election nightmare scenario

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.

But that isn't a guaranteed result.

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.

There are dozens of ways for the College to tie, given the 51 moving parts: the 50 states (each state assigned a number of electoral votes equal to the total of its House and Senate delegation) and the District of Columbia, assigned three electoral votes by constitutional amendment.

However, most of the ties are nonsensical, since most states have an established tilt to one party or the other. California will not go Republican, and Texas will not vote for the Democrat.

Yet take a look at the current electoral college map, which is based both on historical trends and this month's polls:

The totally safe and likely states for Obama have 200 electoral votes. For McCain, the similar total is 174... BBC