John G. Nicolay, A Short Life of Abraham Lincoln, condensed from Nicolay and Hayes' Abraham Lincoln: A History

[364] McClellan after the Peninsula disaster, commanded the left wing of the Army of the Potomac at Antietam. He was not covetous of the honor now given him. He had already twice declined it, and only now accepted the command as a duty under the urgent advice of members of his staff. His instincts were better than the judgment of his friends. A few brief weeks sufficed to demonstrate what he had told them — that he “was not competent to command such a large army.”

The very beginning of his work proved the truth of his self-criticism. Rejecting all the plans of campaign which were suggested to him, he found himself incapable of forming any very plausible or consistent one of his own. As a first move he concentrated his army opposite the town of Fredericksburg on the lower Rappahannock, but with such delays that General Lee had time to seize and strongly fortify the town and the important adjacent heights on the south bank; and when Burnside's army crossed on December II, and made its main and direct attack on the formidable and practically impregnable Confederate intrenchments on the thirteenth, a crushing repulse and defeat of the Union forces, with a loss of over ten thousand killed and wounded, was the quick and direful result.

It was in a spirit of stubborn determination rather than clear, calculating courage that he renewed his orders for an attack on the fourteenth; but, dissuaded by his division and corps commanders from the rash experiment, succeeded without further damage in withdrawing his forces on the night of the fifteenth to their old camps north of the river. In manly words his report of the unfortunate battle gave generous praise to his officers and men, and assumed for himself all the responsibility for the attack and its failure. But its secondary consequences soon became irremediable.