I don’t think that’s the real issue, although it may be a factor as well.
Incumbent presidents have the upper hand, in general. Obama in particular is a bright guy with a likeable personality, which is a huge huge advantage, IMO. He’s not too popular now because 1) the economy has not recovered, and 2) he’s spent an enormous amount of money and made huge changes with no apparant positive results.
But the economy goes in cycles. By 2012, it’s likely to be better than it is today regardless of anything Obama does, and Obama will remind everyone again and again that in 2008 we were about to go into a Great Depression due to the Bush policies, until he came along and saved the day. And he’d like to have solved even more of our problems but when you consider how truly disastrous the Bush policies were you realize how far we’ve come. Plus if the Republicans win control of the House, that will be another reason why Obama has not made as much progress as he would like to have, but look how much he’s actually accomplished in the face of these obstacles.
Add it all up and my money is on Obama, regardless of the ideology of whoever runs against him. Though obviously a tea-party oriented person will find it even harder.
So far, I’ve not really seen this tea party phenomenon as a big deal, in terms of presidential politics. None of the major names being bandied about are TP, AFAIK, other than Palin, and I don’t think she’s a legitimate contender.
So far the only place I can think of where the TP has had the type of impact you describe is Harry Reid’s Senate seat. (Though I may have missed something.)