McClellen ran, as the Democratic President candidate, on a plank that called for a negotiated end to the war. He did not believe that crushing the Confederacy was the way to end the war. I agree, he also lacked the killer instinct that proved necessary in the end to win.
A plank that McClellan himself had repudiated. And even had McClellan won he would not have taken office until March 1865. What president would surrender to the opposition when they were within a hairs-breadth of winning the war?