“The U.S. and the Holocaust,” the latest big PBS documentary from Ken Burns , is a different sort of film for him in that — unlike “ Baseball ” or “Jazz” or “ Benjamin Franklin ” — it seems very much a response to current events, made not just as a commemoration but as a warning . American nativism, xenophobia and white supremacy, having been given cover by the previous president, are renascent; the Anti-Defamation League found a 61% increase in attacks on Jewish institutions from 2020 to 2021. Burns (with co-directors Lynn Novick and Sarah Botstein) will make that...