This is a double rarity, first because it approaches the topic of McClellan from an exclusively political perspective; second, because it treats his politics with respect and sympathy.
It is, in these times, unimaginable that anyone could have had the bad taste to run against Lincoln, even though Lincoln had rafts of would-be opponents, both Republican and Democrat. This is not easily digested, but Waugh makes it palatable. His symapthies are interesting, the Democrats, esp. McClellan, coming off slightly better than the Republicans. And this is done without particularly slighting Lincoln himself.
The structure of the book is that of a political thriller. The power of the narrative, the fascination offered by its vaious details, draws us into this suspense even though we know the outcome. In fact, Lincoln's reelection emerges as utterly improbable, whence the suspense. If the book has weaknesses it is in the overloaded descriptions of some historical personalities and movements that collapse before they can merit narrative weight; it is also in the bare-bones depiction of McClellan's political ideas and the tendency to make McClellan no more than a representative of the best Democratic thinking of 1864, when he was much more. And it is in the scant mention of those schemes that would have restored McClellan to command of Union forces in 1863 or 1864, taking him out of the political arena.
Outside of the qualified exception of Korea and Ike, I can think of no American war during which a military senior, on the presumption of civilian mismanagement, ran against the president for the highest office in the land. This may chill current sensibility to the bone, but not Waugh's. McClellan's opposition is portrayed as not only principled, but possibly even admirable.
McClellan was an extraordinary American intellectual whose first interest was military theory and practice and whose later interest was government. The political McClellan is only slightly better known through Waugh, but thank heaven for small favors. Meanwhile, the entertainment value Waugh provides is a very big favor.