Lincoln now magnanimously gave General McClellan another and a splendid opportunity to achieve success. His command embraced the army of the Potomac, the remains of the army of Pope, and the troops of Burnside, while to these were added the large number of recruits and volunteers which poured in from the loyal states, so that he had, before November, more than two hundred thousand soldiers under his command.
If he had possessed to any extent the elements of a hero, if he could have led a rapid and brilliant campaign, he had now the opportunity, and the people would have eagerly crowned him with the laurels of victory. But as soon as he was settled in his command, he continued to make the old complaints and calls for more troops. He wished those engaged in the defense of Washington sent to him, even if the capital should fall into the hands of the enemy.
Colonel Miles and General Julius White, in September, 1862, occupied the picturesque village of Harper's Ferry, with some twelve thousand soldiers. On the 11th, McClellan asked that these troops be directed to join his army. That order was not given, but it was suggested to him that he open communication with Harper's Ferry, and that then these troops would be under his command. On the 13th, he knew that Lee's army was divided, and that Jackson had been detached from the main army for the purpose of capturing Harper's Ferry. McClellan by promptness could have saved Harper's Ferry. Swinton, who excuses him when he can, says: "If he had thrown forward his army with the vigor used by Jackson... he could have relieved Harper's Ferry, which did not surrender until the 15th." Palfrey, in his "Antietam and Fredericksburg," says: "He was not equal to the occasion. He threw away his chance, and a precious opportunity of making a great name passed away."
On the 17th, was fought the bloody battle of Antietam. Of this battle, alluding to McClellan's delay in attacking while Lee's forces were divided, Palfrey says: "He fought his battle one day too late, if not two." "He did very little in the way of compelling the execution of his orders." A very large portion of his army did not participate in the battle, and Palfrey adds: "It is probable, almost to a point of certainty, that if a great part of the Second and Fifth corps, and all the Sixth, animated by the personal presence of McClellan, had attacked vigorously in the center, and Burnside on the Federal left,... the result would have been the practical annihilation of Lee's army!"
McClellan, against the advice of Burnside and others, decided not to renew the attack on the 18th. "It is," says Palfrey, "hardly worth while to state his reasons." Two divisions had joined him. "The fault was in the man. There was force enough at his command either day had he seen fit to use it." By the time that McClellan got ready to renew the attack Lee was gone. On the 18th, the enemy were permitted to retire across the Potomac. The Union army slowly followed, occupying Maryland Heights on the 20th, and Harper's Ferry on the 23d of September. On the 7th of October, Halleck telegraphed to McClellan that "the army must move. The country is becoming very impatient at the want of activity of your army, and we must push it on."
The President was also impatient at these slow movements of McClellan, and to a friend of the General's who called at the White House, he said, doubtless with the expectation that it would be repeated: "McClellan's tardiness reminds me of a man in Illinois, whose attorney was not sufficiently aggressive. The client knew a few law phrases, and finally, after waiting until his patience was exhausted by the non-action of his counsel, he sprang to his feet and exclaimed: 'Why don't you go at him with a Fi Fa, demurrer, a capias, a surrebutter, or a ne exeat, or something; and not stand there like a nudum pactum, or a non est?'"
By the 6th of October, the President's impatience of McClellan's long delay induced him to telegraph the General: "The President directs that you cross the Potomac and give battle to the enemy or drive him South." McClellan did not obey. On the 10th, Stewart, a rebel cavalry officer, crossed the Potomac, went as far as Chambersburgh in Pennsylvania, made the circuit of the Federal army, and re-crossed the Potomac without serious loss. This was the second time Confederate cavalry had been permitted to ride entirely around McClellan's army. On the 13th of October, the President made one more effort to induce McClellan to act, by writing him a long and kindly personal letter.