Well according to some political theories (which I happen to believe in) in order for Obama to be defeated in the next election two distinct and different circumstances must occur:
1. The voting public must be sufficiently dissatisfied with Obama
and
2. The voting public must be presented with an alternative candidate that offers a significant difference.
Without both of these occurring, the incumbent stands a very good chance of being re-elected.
Consider the 2004 elections. Bush's approval rating was very low and his disapproval rating was high. This satisfied the first requirement.
However, the Democrats, in the form of Kerry, failed to demonstrate that Kerry would be a significant change (improvement). Kerry ran on mostly an "I am not Bush" platform.
Not being the incumbent is rarely enough for the voting public to choose to nor re-elect the incumbent. The result: Bush was re-elected
Fast forward to 2012
Obama's approval rating may be low and his disapproval rating may be high by the time of the elections.
But is the Republican party able to field a candidate that offers the voting public a significant improvement? That is the question that will govern this election. If the Republicans fall into the same trap as the Democrats did in 2004 and run a 2012 candidate on the "I am not Obama" platform, Obama may have a good chance of being re-elected.
Personally, as a Recovering Republican and an Extreme Moderate Independent, I have not seen the GOP satisfy the second part of the theory.....yet.
It is still early and we are still stuck with the seven dwarfs fighting among themselves, but soon the GOP will have to decide on who they want to represent their party in the next election and start building a platform that consists of more than "I am not Obama".
And by soon, I think by the time of the next election which is on Tuesday.

. Republican primaries start in Jan 2012. Not a lot of time!
I will be waiting and watching as I am sure the rest of us will be.