Do undecided voters break for the challenger?<quoted text>
Actually you are incorrect. undeceided votes usually go with the incumbant. So add 8% to Obama to 53%.
Ther that's a little more accurate.
When pollsters interpret results for a race involving an incumbent, pollsters have typically applied the rule that incumbents rarely get a higher percentage in the election than they receive in polls, and that voters still undecided on the very last poll tend to "break" disproportionately for the challenger.
Also, click on this link to display a listing of all posts concerning the incumbent rule on Pollster.com (in reverse chronological order - most recent first). This link display posts on the incumbent rule from the blog MysteryPollster.