Coolidge: An American Enigma. This is a book review by Florence King. It was published in National Review, August 17, 1998.
From the site:
FINDING that elusive last piece of the puzzle that was Calvin Coolidge has frustrated historians for 75 years. Robert Sobel fares no better than the rest, but he has a knack for digging up obscure quotes that illustrate the unusual scope of the frustration. The best of these comes from a now-forgotten journalist who called Coolidge ''one of the two great enigmas of the first third of the twentieth century, the other being the popularity of the play Abie's Irish Rose.''
Sobel, a professor of business history at Hofstra University, has put together a book that, like Coolidge himself, makes no claim to be other than what it is. He readily admits that he did no original research and has no new revelations to offer, but his familiarity with secondary sources and his expertise in mining them for their most trenchant contributions make Coolidge: An American Enigma both an informative text and a consistently readable story.