Michael Barone is always worth reading. I think he's wrong in prematurely judging the surge a success, but this is an interesting insight:
Somewhere between Hurricane Katrina in August 2005 and the bombing of the Samarra mosque in February 2006, I believe we entered a period of open-field politics, in which voters and candidates are moving around -- a field in which there are no familiar landmarks or new signposts.
Those were the headline stories that showed that government was broken at home and that the Iraq occupation would be for ever. Voters want a competent government and no Mesopotamian empire. Who can give them both?