As a military success the battle of Antietam demanded to be followed up.  Reinforcements had now come to McClellan, and Lincoln telegraphed, “Please do not let him get off without being hurt.”  Lee was between the broad Potomac and a Northern army fully twice as large as his own, with other large forces near.  McClellan’s subordinates urged him to renew the attack and drive Lee into the river.  But Lee was allowed to cross the river, and McClellan lay camped on the Antietam battlefield for a fortnight.  He may have been dissatisfied with the condition of his army and its supplies.  Some of his men wanted new boots; many of Lee’s were limping barefoot.  He certainly, as often before, exaggerated the strength of his enemy.  Lee recrossed the Potomac little damaged.  Lincoln, occupied in those days over the most momentous act of his political life, watched McClellan eagerly, and came to the Antietam to see things for himself.  He came back in the full belief that McClellan would move at once.  Once more undeceived, he pressed him with letters and telegrams from himself and Halleck.  He was convinced that McClellan, if he tried, could cut off Lee from Richmond.  Hearing of the fatigue of McClellan’s horses, he telegraphed about the middle of October, “Will you pardon me for asking what your horses have done since the battle of Antietam that tires anything.”  This was unkind; McClellan indeed should have seen about cavalry in the days when he was organising in Washington, but at this moment the Southern horse had just raided right round his lines and got safe back, and his own much inferior cavalry was probably worn out with vain pursuit of them.  On the same day Lincoln wrote more kindly, “My dear Sir, you remember my speaking to you of what I called your over-cautiousness.  Are you not over-cautious when you assume that you cannot do what the enemy is constantly doing?  Change positions with the enemy, and think you not, he would break your communications with Richmond within the next twenty-four hours.”  And after a brief analysis of the situation, which seems conclusive, he ends:  “I say ‘try’; if we never try we shall never succeed. . . .  If we cannot beat him now when he bears the wastage of coming to us, we never can when we bear the wastage of going to him.”  His patience was nearing a limit which he had already fixed in his own mind.  On October 28, more than five weeks after the battle, McClellan began to cross the Potomac, and took a week in the process.  On November 5, McClellan was removed from his command, and General Burnside appointed in his place.

Lincoln had longed for the clear victory that he thought McClellan would win; he gloomily foreboded that he might not find a better man to put in his place; he felt sadly how he would be accused, as he has been ever since, of displacing McClellan because he was a Democrat.  “In considering military merit,” he wrote privately, “the world has abundant evidence that I disregard politics.”