Sawzaw, simply as a point of information: the results of a public opinion poll, no matter how scrupulously conducted, say nothing about what the actual likelihood of success or failure (however these are defined) may be.

The poll only measures the level of confidence of the respondents. But I doubt they have much expertise or any first-hand knowledge.

And what might be "success" for one person (say, "a stable, neutral Iraq") might well be "failure" for someone else (who, for example, might demand "a stable, democratic, U.S.-aligned Iraq").

Opinion polls measure opinions and little else, and they don't always do that very well.