Here is a blog by an American officer that tells us the Iraq war from inside.
The war cannot easily be summarized. If it could be, he would summarize it for us. But we are clearly winning, it is clearly costing, Iraq remains all @#$%^&*, and is likely to rapidly become more @#$%^&*, the moment US troops leave. Clearly Iraq is not going to become a Jeffersonian democracy any time soon, but looks increasingly probable it will not be overrun by Islamic radicals the moment US troops leave.
On the one hand, nation building has not been a total failure. On the other hand, it is taking a lot longer, costing a lot more, and producing a lot less than had been promised.
The problem is that after this experience, it is not a credible to threaten that tyrants who attack Americans, or sponsor terrorists who attack Americans, are going to suffer overthrow followed by nation building