Have the present-day progressives who say they admire him ever read him? The American Left has an abiding attachment to Theodore Roosevelt. Everyone from MSNBC anchor Chris Matthews to former Harvard University Press editor-in-chief Aida D. Donald keeps Roosevelt on hand as a stand-in example of a “good Republican” — invoked, perhaps, when the name of Abraham Lincoln has been outworn, and a new exemplar of “acceptable” Republicanism is needed. A “trans-partisan” figure and an original “progressive,” Roosevelt represents what the GOP could have been. But on the social issues that loom so large in the liberal Democratic mind, just...