Reagan: His Life and Legend, by Max Boot, Liveright, 836 pages, $45 Max Boot believes “the biographer’s job is to find the compromises and expose the shibboleths and then to report on them dispassionately, not to cover them up or exaggerate their importance, so that readers can make up their own minds.” In Reagan: His Life and Legend, the first comprehensive biography of President Ronald Reagan since Donald Trump entered the White House, the historian and Washington Post columnist mostly succeeds at that. But understanding Reagan through the lens of Trump does at times lead the author astray. …