Whoever thinks the Iraq war didn’t have anything to do with the Republicans losing Congress is naive and are fooling themselves. Yes, there were other factors but the Iraq war was one of the major ones. Granted the media, day after day was rooting for the Republicans to lose Congress and did all they could to emphasize corruption and scandals. CNN was close to outright on the side of the Democrats wanting a party change. But the steady drumbeat of bad news coverage from Iraq really sealed the coffin.
You might add that the MSM have mining for Republican bad behavior for six years in hopes of finding something that would stick.