That's what the American people are thinking too, which is why they are going to vote him out of office in the 2012 Presidential election. If he decides to run again that is. He could conceivably decide not to. If he does quit it won't be because he's tired or stressed out or wants to spend more time with his family. Those would be rationalizations. The real reason would be that his ego and self-image wouldn't allow him to face certain defeat. Quitting in the face of ignominy and adversity would be entirely in character and the possibility of it happening shouldn't be discounted at all. The "one term is enough" remark was no accident. It was made on purpose and was an attempt to test the water, to see what the reaction would be.
Obama's record in office has been atrocious and he has nothing to offer the electorate except empty excuses and pious platitudes which have no weight or meaning in the real world. Americans recognize and understand that he is incompetent and simply not capable of being an effective President. They know that he has caused enormous damage to the country itself and to them as individuals and that there would be more of the same if he were given a second term...domestically and internationally he has been an unmitigated disaster and nothing would change the second time around. They also know that he is duplicitous, smarmy, weak, supercilious, conniving and has an ideology and mental set that is fundamentally at odds with American values and principles, including the rule of law. That won't change the second time around either.
Obama is going to be a "one and done" President alright, either because he'll choose not to run again or because he'll lose the election if he does. That's what elections are for after all. Righting the ship' and throwing the bums out and that is exactly what's going to happen in 2012.
My bet is that he will quit as soon as he concludes that he cannot be re-elected. In the meantime we must all do whatever we can, legally and ethically of course, to prevent him from doing even more damage than he's already done.