Several polls also showed McCain competitive in OR and MI. We all know how that turned out in the end....
Remember, McCain withdrew his campaign from Michigan in mid-September, effectively handing the state over. I remember one poll some time around March that showed him tied with Hillary and losing to Obama here, and another one later that showed him beating them both. Then Obama took the lead in nearly every Michigan poll after he secured the nomination.
Because McCain was seen as a more moderate, conciliatory conservative, he would have won in any year before 2008 by a solid margin. But by the time he was nominated, nearly the entire country had come down with severe Bush Derangement Syndrome, and his chances were almost entirely shattered. He took the lead after the convention, but then the financial crisis destroyed whatever chance he had left.
NO Republican would have won in 2008, given Bush's abysmal approval ratings and the financial crisis. But McCain did exacerbate the situation by picking Palin as his running mate, one of the single most reckless decisions made by a presidential nominee in history (2nd to McGovern picking Eagleton). Then, when Lehman went bankrupt and the world was in panic, McCain acted like an unstable old man by suspending his campaign so he can return to DC to work on the problem. Of course, McCain knows very little about the economy and added no value when he went back to DC. In contrast, Obama exuded a sense of calm leadership, even temperament, and good judgment. It of course did not hurt that Obama decisively won all 3 debates against the old mumbling McCain. If it weren't for those grievous errors, McCain's margin of defeat would have been more like 3-4 points nationally rather than 7.2 points. And he would have won IN, NC, FL, NE 02, and the GOP would have done better in the congressional races as well.