(fm the BC thread "Kilcullen vs Sullivan")
(images fm Wiki)
One of life's ironies is that as the Secession crisis came to a head Sherman was an employee of the State of Louisiana as head of the Military Academy. He could not offer his services to the Union until after he had resigned his position. In fact he knew the South well having been stationed there in earlier years.
The mirror of that situation was Robert E. Lee being at the same time the commanding officer of a Union post in Texas and determined to honorably carry out his duties and defend his command. In fact after the surrender of the Union establishment to the seceding State of Texas Lee travelled to Washington and accepted an appointment as a Colonel signed by Abraham Lincoln and served until Virginia left the Union, departing only when his resignation was accepted.
George McClellan did good work. He built the army that Grant fought with. Some are best at training, some at logistics, some at strategy, and some at tactics. Few are good at all. Sherman was a better strategist than tactician. McClellan was better at logistics and training and administration. That does not make him unworthy or traitorous, just human.
I am leaning over to be fair to McClellan, criticize that as you wish. He publicly disputed the Democratic platform and declared his intention to preserve the Union. Given who he was fronting for his election would probably have lead to disunion followed by an authoritarian crisis. It was a very near thing and I am glad that Lincoln won. Nevertheless I do think that "Little Mac," who did care for his troops, was not a traitor. We all want to talk about the dashing cavalry hero but the fact is that the military is a bureaucracy and the great administrators in history may not get any movies of their lives or girls dreaming of them but they build the machine that achieves victory.