From a perspective of 150 years, it would appear that the overarching problem between McClellan and Lincoln was Lincoln's inability to articulate the strategy of the war as perceived by himself, and therefore McClellan's inability to approach the war as a federal official suppressing a traitorous revolt by upstart rebels. As a result, McClellan's dallying and failing to pursue Lee aggressively led to a tacit recognition of the validiity of the CSA military as a legitimate army. It was almost as if McClellan had de facto recognized the CSA as an entity. Which of course enraged Lincoln. And also explains why Lincoln was so deeply relieved when Grant finally took command along with Sherman, and advised Lincoln that they would approach this as an unconditional effort to suppress a revolution. Lincoln's statement that "This man fights!" was no casual comment; he needed a general who would chase the last active rebel to hell and back until every active rebel was hanged. McClellan was never of this mindset, even in the waning days of the war.