Some of the most serious of the perplexities that came upon Lincoln during the first two years of the War were the result of the peculiar combination of abilities and disabilities that characterised General McClellan.  McClellan’s work prior to the War had been that of an engineer.  He had taken high rank at West Point and later, resigning from the army, had rendered distinguished service in civil engineering.  At the time of the Lincoln-Douglas debates, McClellan was president of the Illinois Central Railroad.  He was a close friend and backer of Douglas and he had done what was practicable with the all-important machinery of the railroad company to render comfortable the travelling of his candidate and to insure his success.  Returning to the army with the opening of the War, he had won success in a brief campaign in Virginia in which he was opposed by a comparatively inexperienced officer and by a smaller force than his own.  Placed in command of the army of the Potomac shortly after the Bull Run campaign, he had shown exceptional ability in bringing the troops into a state of organisation.  He was probably the best man in the United States to fit an army for action.  There were few engineer officers in the army who could have rendered better service in the shaping of fortifications or in the construction of an entrenched position.  He showed later that he was not a bad leader for a defeated army in the supervision of the retreat.  He had, however, no real capacity for leadership in an aggressive campaign.  His disposition led him to be full of apprehension of what the other fellow was doing.  He suffered literally from nightmares in which he exaggerated enormously the perils in his paths, making obstacles where none existed, multiplying by two or by three the troops against him, insisting upon the necessity of providing not only for probable contingencies but for very impossible contingencies.  He was never ready for an advance and he always felt proudly triumphant, after having come into touch with the enemy, that he had accomplished the task of saving his army.

The only thing about which he was neither apprehensive nor doubtful was his ability as a leader, whether military or political.  While he found it difficult to impress his will upon an opponent in the field, he was very sturdy with his pen in laying down the law to the Commander-in-chief (the President) and in emphasising the importance of his own views not only in things military but in regard to the whole policy of the government.  The peculiarity about the nightmares and miscalculations of McClellan was that they persisted long after the data for their correction were available.  In a book brought into print years after the War, when the Confederate rosters were easily accessible in Washington, McClellan did not hesitate to make the same statements in regard to the numbers of the Confederate forces opposed to him that he had brought into the long series of complaining letters to Lincoln in which he demanded reinforcements that did not exist.