I'm not puzzled by McClellan.
I'm puzzled by some who attack him for his participation in what he later blew the whistle on.
Seems to me that's what, for instance, John Dean did or many during and after Vietnam, all defectors to either side, etc.
Why would the left attack McClellan? Same reason they attacked McNamara, I suppose. Who came to the party very late. However, even deathbed religious conversions are accepted and honored, at least here on Earth.
Arf