I still think the decision was right, but the strategy wrong.

1) Lots of time spent planning defeating Saddam's army, almost none planning aftermath.

2) Troup strength.

3) Dismissal of insurgency as a real issue instead of jumping on it early.

4) Al-Sadr

5) Securing boarders.

6) Lousy way to build a government. The iraqi government is a mess in part because of how it was elected. It's practically designed for sectarian strife. Voting for slates of candidates rather than individuals assures more of a least common denominator than an election of leaders IMO.

7) Probably most of all - slow reaction and slow to change strategy. A problem that is obviously continuing. This is a situation that needs daily reaction on average and minutes at times not annual reaction or election cycle reaction speed.