Polls tighten
The only real poll is Tuesday.It is much closer than most pollsters admit. Some of those polls have been overweighted in favour of Dems which is why Obama was "leading". Now that the election is near, they are in CYA mode. In 2004 the exit "polls" showed Kerry was leading but he actually lost.
Some history....
http://www.washingtonpost.com/wp-dyn/articles/A22188-2005Jan19.html

