Blair, yes I'd say Iraq did bring him down.

Certainly until Iraq he had an almost spotless (or as close to you get after half a decade as the most prominent face in UK politics) record especially with the economy, for Labour to only lose 5 seats in 2001 was nothing short of stunning and was representative of Labours success as much as the Conservatives weakness. I think this determination to act like a head of state rather than a prime minister grated inside Westminister much more than it did outside. By the end of course there was a turning of the tide against him publicaly (although not enough to lose him the election) but that was largely down to the view that he lied to the public to get rid of Sadam, without that the 2005 election would have been far more convincing.

I don't think Iraq brought down Labour (it was general fatigue, Browns strength the economy becoming a stunning weakness and his poor public relations long after Blair left), Blairs downfall came towards the very end of tenure and largely after (Fern Britton for example).