Commentary At the end of his magisterial book “How Rome Fell: Death of a Superpower,” Adrian Goldsworthy compares the fate of imperial Rome with contemporary America. The dominance of a civilization, he notes, depends not only on resources and military prowess but also on “culture,” that hard-to-define yet palpable mixture of confidence, savoir-faire, and commitment to foundational principles beyond the calculus of individual profit or aggrandizement. Beginning in the third century, Goldsworthy writes, Rome began to turn away from that cultural compact and decline wove itself into the sinews of Roman society. “The rot,” Goldsworth observes, “began at the top, and in time a similar attitude pervaded the entire government and army high command.” I predict that future historians, seeking to understand the decline of the United States, will settle on the annus horribilis of 2021 as the terminus a quo.  Immersed in the moment, it is often hard to disentangle …