I know people will bemoan McClellan’s lack of loyalty to his former employer. But it’s important to keep in mind that when your boss abuses his/her power, to the detriment of the common good (especially when it leads to the deaths of hundreds of thousands of people, ruins the economy, etc.), then you have an obligation to speak out.
It would have been helpful if he had come out sooner about this, but I suppose he wanted to get his point across in a detail-rich book, and not sound like a Hyde Park ranter.
And, fortunately, he’s done so before the election, one in which one of the candidates has received a warm endorsement from George W. Bush.
You can get the book from Amazon (currently ranked #1).