A lot of that depends on what the environment is at the time. Will the country be talking about debt or will we be talking about some mythical "jobs bill" or some other issue. Nothing can stay forefront in the news forever, the media moves from issue to issue and a lot depends on what captures the public's interest.
Further, this is not the same country as it was in the past. The American population is much more dependent on government and will likely vote more and more like Europe. 47% now pay no income taxes, 48% are in some way dependent on government transfer payments. Where once upon a time people felt screwed by a bad economy and wanting to give the new guy a try, now they are living off government money and have far less incentive to do that - worse, the dependence this creates makes it far LESS likely they would vote for someone who threatened to curtail or eliminate their freebies.
You are absolutely dreaming if you believe Obama will be easy to beat. He will get no less than 45% of the vote, and it is far more likely he will be closer to 50%. If I had to guess 2012 will be close, along the lines of 2004 - if we nominate someone that can't hold up through a tough election we will lose.