De jure federalism and de facto partition should be a U.S. goal for Iraq. For example, I like this proposed strategy. (For comparison, you might like to peruse this Foreign Affairs roundtable on Iraq.) I would add to that NYT op-ed that partition is compatible with a goal of democratic Iraqi government; it just recommends more focus on local political institions.

I see two problems with the partition strategy: fighting over oil revenues and an impractical desire among both many Iraqis and American policymakers for a more united Iraq. I don't have much to say about the first problem. As for the second, according to polling from late June, three fourths of Iraqis oppose ethnic or religious segregation of their country, even in Baghdad. On the other hand, Randall Parker points to evidence of people voting with their feet for segregation. (More here.) If the communal violence goes on long enough, all the major players will settle for a partition, provided the oil issue is resolved.