Ross Douthat is out with the theory that these Bigwig Young Darlings of Left - messers Ezra Klien, Jonathan Chait and others - opted for saying 'sorry' rather than being intellectually honest to acknowledge inherent help Bush's failed Iraq War gave to the success of Democrats in recent years. Better to be humble than expose true reasons of your success - someone else's foolishness and incompetence.
The problem with this theory is to assume otherwise is basically to assume that American Democratic System fails to work. Imagine that after all this bungling of Iraq War, people still vote Republican Party. That would mean we would not have any other political party viable to conduit People's Will and make a run for change. If you have an argument that there should be more than 2 political parties in USA and then Americans would have had an opportunity to vote someone different than Democrats; then say so.
For good or bad, we have duopoly in our system. With Daily Kos, Huffington Post, FireDogLake, Talkingpointsmemo and all those brethren on Left thriving on anti-war sentiments essentially transformed Democratic Party culminating in foisting of Nancy Pelosi as the speaker in Dem House victory of 2006; exactly the same way Tea Party propelled "Shellacking of Barack Obama in 2010" has been a genuine attempt to change GOP (whether I agree with Tea Party policies and politics, that is a different issue).
What Ross is offering is history and plain vanilla 'description' of how events unfolded in the last decade. It is useful and very insightful reading of contemporary American History, but that cannot be lessons of Iraq War. If not Iraq War, then something else (2008 recession? no mention of that? McCain's theatricals of halting 2008 campaign as a response to 2008 financial crisis?) would have given an equally potent reason to all these emerging 'political forces in America' to express themselves on behalf of changing demographics of America.