The independents went democrat because of the misrepresentation of the Iraq war by the media.
And that misrepresentation was allowed to happen by the President. He allowed the media to frame the debate. He was purely reactionary. The times he would talk, he only put it in terms of what was good for the Iraqis. Boil it down and most Americans don't give a whit about Iraqis getting electricity or clean water. They want to know what's in it for them.