Not at all. How many incumbents that were elected (not appointed such as Ford) actually lost a Presidential race over the past 80 years? Exactly two! Jimmy Carter and George Bush (Sr.) And the only reason Bush lost was because there was a more conservative candidate running in 1992, Ross Perot who garnered 19% of the vote, most of which would have gone to Bush.
So the only other elected incumbent to lose in a two way race was Jimmy Carter. And he lost because he was perceived as weak on foriegn policy because of the Iran hostage crisis. And also very ineffective with fiscal policy (note inflation at 16%, gas lines, and interest rates at 18%).
One other important historical notation. It took the likes of Ronald Reagan to oust Carter. When someone looks at a sitting President and claims that he will be easy to beat they're dead wrong. There is a reason that sitting Presidents who run for reelection usually win. They have control of the government and can bring powerful forces to bear on the population which can influence their vote. And that's not even counting the MSL media which will be out in full force to reelect their chosen one.
Can Obama lose? Yes. But, it will take almost the perfect candidate running the perfect campaign along with a continuing slumping economy to beat Obama. And then it will still be a squeaker for many of the reasons I mentioned along with the fact that Obama will have a larger war chest.
Many Obama haters (of which I am one) find this difficult to believe because THEY think the President is doing a poor job (and he is). But there are millions of people (and organizations) who are the recipients of big government aid, in some form, who will turn out in droves to support Obama. Along with the African American population that will vote for Obama regardless of what he does.
More salt to the wound, if Obama dumps Biden and takes on Hillary as his VP that will place him in the almost impossible to beat category.
On a brighter note, every Presidential election is either won or lost electorally on a state by state basis. So look for key states like Ohio, PA, Fla, Illinois and others to tell the tale early on. Right now Obama's poll numbers are slumping badly in these (and other) key states, so there is a window of opportunity, if the economy continues to be brutal in certain states. And finally there are more republican governors this time around than in 2008, that too adds to the republican nominees chances. As a republican governor, it is said, can add up to 3% (or more depending on his popularity) to the republican nominees chances.
But unfortunately at this point in time Obama is the odds on favorite in my opinion.