Because judgments of probability are made on the basis of prior knowledge, the same piece of information can either confirm or disconfirm a given hypothesis depending on one’s presuppositions. This is not a theoretical possibility. It happens all the time and goes a long way to explaining how contradictory political views can persist in the face of uncontroverted evidence. Different judgments reflect different values, but they are also rooted in contrasting factual beliefs.
The application: right-wingers not only believe that America ought be the unquestioned paramount power in the world; their foreign policy proposals only make sense if we are and will remain vastly more powerful than the other nations for the foreseeable future. Recent events have shown that this notion is at least questionable. In theory, the contrary evidence might change minds; but in practice, believers in American exceptionalism are more likely to explain away failures by recourse to ad hoc supplementary hypotheses. Recall the precedent of 1918. When defeat on the battlefield challenged the presumption of their invincibility, the Germans could have acknowledged that they had been overmatched. Instead, they devised the Stab-in-the-Back story. The analogous salves to pride are currently under construction in the conservative think tanks, and prototypes are tested nightly on Fox News. The narrative about domestic cheese-eating surrender monkeys will make it possible to interpret each new disaster as further proof that we were right all along. After all, it’s obvious that only a womanish failure of nerve and a neurotic obsession with legalistic scruples stands between us and ultimate triumph.