Err neg---realism is a descriptive label attached policies only after they have been proven to be successful

Mearsheimer understands this problem when he says that when states behave in ways that defeat their interests, it embarrasses his theory, 64 and it is the very discrepancy between what he and Walt see as the dictates of realism and the policies the United States followed that motivate these books and their earlier critique of US policy in the Middle East. But when we see realism can be prescriptive rather than descriptive, then national misbehavior no longer necessarily disconfirms the theory. While it does have to be explained or at least considered, it does not dispute the claim that the state would have secured better outcomes had it followed realist precepts. Thus Waltz argues that states that ignore realism will “fall by the wayside,”65 and while the evidence for the proposition is limited, it has the advantage of separating prescriptive and descriptive aspects of the theory.

The separation creates and solves problems, however. For one thing, it raises the question of how often states in fact behave in a realist fashion, and since realism is more a school of thought and a general approach than a tight theory it also raises the possibility that realist scholars will attach this label to successful policies and deny it to failed ones. (I wonder if our explanation and evaluation of the US invasion of Iraq would have been different if Saddam did in fact have advanced WMD programs and plans to use them.) For another thing, it implies we scholars are smarter, or at least more knowledgeable, than decision makers. We can avoid this self-serving and implausible claim by arguing that leaders are often unable to work toward the national interest because they are thwarted by domestic politics, pathologies in society, or impediments to rational decision making. Of course one would want to specify when, why, and how states are led astray,66 and even if these claims are subject to dispute, they make clear the limits of realism’s ability to explain national behavior.