Although he’s primarily (if reductively) identified with gangsters and New York City, Martin Scorsese has long expressed an interest in directing a Western. John Ford’s The Searchers serves as a particular touchstone — Harvey Keitel delivers a lengthy disquisition on the film in Scorsese’s first feature, Who’s That Knocking on My Door, and Taxi Driver consciously evokes its plot — but Scorsese adores the genre in all its permutations and periods. In Killers of the Flower Moon, the 80-year-old auteur at last realizes that delayed ambition.