YORBA LINDA, California — Fifty yards from Richard Nixon’s grave, which sits not quite in the shadow of the modest home where he was born, a series of exhibits at his presidential library describe him as a psychologically unbalanced fool. The Nixon White House, museum display panels announce, was consumed by “a climate of deep suspicion.” The infamous Plumbers took action against “perceived political opponents within the Federal Government.” A video display allows visitors to choose clips on the theme of Nixon’s “Conspiracy Thinking.” Paranoid, the president mindlessly lashed out at enemies that he hallucinated. This is still the official...