Hooker had initiated the day’s battle with tremendous intensity, but he was now off the field. Mansfield was dead, and McClellan, counting the wounds to his regiments and divisions, was becoming terribly cautious. Even so, McClellan cannot be blamed for the poor performance by General Ambrose Burnside.

Burnside had roughly twenty thousand men, leading the left flank of the Union force. He was in no possible danger—the fighting was all to his right (or to the north), and he was under orders to take the bridge that would bring his men into the battle. Why Burnside fumbled so badly on this occasion is not fully known, but he did not have his men in motion till 2 P.M., and the bridge was not taken until two hours later. The Confederates prudently withdrew, and Burnside was satisfied with occupying the ground on the west side of Antietam Creek. None of the top Union commanders seemed to realize that complete victory was within their grasp. One vigorous attack from the Union center would, very likely, have brought about a complete Confederate collapse.