No concept like American Exceptionalism can long survive, minus a foundational, common understanding and appreciation of absolute Truth. Don't get me wrong. I don't believe it's necessary for everyone in the world -- or even everyone in a given nation to absolutely believe in the same core dogma, in order to become or to remain exceptional, in one or more ways. In fact, a common premise in scientific research includes that we often approach the "real" truth, only by questioning accepted truths. However, it has seemed that, with all other things equal: (a) the further that the US has traveled down the path of relativism (e.g., the latest: Common Core Curriculum), the less relevant we have become (as a government) in world affairs and (b) the further that countries' peoples have embraced a common dogma, with apparently little tolerance for relativism (e.g., countries embracing Islam) the more relevant they have become in world affairs. Additionally, I further suggest that this this probably presents as similar to the corporate successes generally associated with creating and maintaining unified organizational visions.
In arguably his best written, but least known, major work, "Discourses on the first decade of Titus Livius," Machiavelli (tr. Thomson, 1883) observed that: "... a democracy tends to degenerate into anarchy (Kindle sec. 29). I wonder if the current state of US affairs otherwise represents a preview of such anarchy and if so, if the ongoing promotion of relativism serves as a primary factor in that transformation.