Oliver Otis Howard, Autobiography of Oliver Otis Howard, major general , United States army : volume 1

On April 1, 1862, the country was divided in sentiment touching the political policy henceforth to be pursued, the majority evidently inclining to the belief that “the Union as it was” could never be restored.

It is not under these circumstances at all unaccountable that Mr. Lincoln's faith in McClellan should have been gradually undermined. McClellan had begun his work when the preservation of slavery was accepted as necessary and, naturally conservative, it was next to impossible for him to modify or abandon an opinion once formed.

Thus McClellan, a soldier of conservative tendencies, promising sincerely to prevent, if possible, the dissolution of the Union, and to preserve or restore that Union as it was before the war, became now, the moment the abolition of slavery as a war measure or otherwise entered as a watchword, the great name around which to rally all the political forces opposed to the party in power.

On the contrary, Lincoln, moving with his party, naturally kept with his political household, while the Republicans gradually passed from their “nonextension” principles to their final stand against all human enslavement. McClellan was, and continued to be, a war Democrat. Lincoln at heart detested slavery and became an emancipator. He personally liked McClellan, but he began to see, prior to Johnston's retreat, that McClellan must gain victories and gain them quickly, or as President he would be forced by an imperious public sentiment to choose another chief. He practically began this (March 11th) by relieving McClellan from the command of all other armies besides that of the Potomac.