I think it's much too early to even rate President Bush's performance. Remember that most historians are overwhelmingly liberal, and so putting Bush among the ten worst presidents is clearly politically motivated. I would probably Bush somewhere in the middle, and Obama just slightly lower.
Given that a lot of historians rank Reagan high, somehow I don't think their politics is the deciding factor.
I agree. My history teacher last semester was fairly liberal, but did feel that Reagan was a good president overall.