At home: disorder in the streets and a rising tide of drugs. Abroad: a shameful, humiliating withdrawal from an Asian outpost of empire. In politics: a conservative demagogue, backed by the silent majority, sweeps aside an ineffectual liberal stooge. In culture: fights over abortion, and women, and music, all conjuring a feeling that the republic is doomed. Am I talking about pot and Saigon and the sweep of Richard Nixon, or fentanyl and Kabul and the return of Donald Trump? I could be...