You don't have any communication between the Israelis and the Iranians. You have all sorts of local triggers for conflict. Having countries act on a hair trigger - where they can't afford to be second to strike - the potential for a miscalculation or a nuclear war through inadvertence is simply too high.
We can't have a failure in Iraq, but we also can't be there for the next 10 years because if we are, it's going to become, I think, a failure in and of itself.