The best thing the US can do now...
is to work as quickly as possible to establish an interim Iraqi government by, of, and for Iraqis. This should be done in the coming weeks, not years. Then, as soon as possible, leave Iraq to its own governance. More than anything else, this will show the Arab world that we aren't there as conquerers or colonists (as if the examples of all the other times we've done this weren't enough). Assistance, by all means, but not governance or occupation.