William Swinton, Campaigns of the Army of the Potomac

As the event proved, it would probably have been a better course to have pushed the pursuit by the direct line, as appears to have been at first intended when Sedgwick, on the 5th, was thrown forward on the Fairfield road. The obstructions which Lee could have placed in the defiles of the South Mountains cannot be considered, as presenting any serious difficulty; for General Smith with a division of militia had moved forward from the Susquehanna, on the 3d, into the Cumberland Valley, and on the 5th he seized and held a pass in the South Mountains, a few miles above that through which the Confederate force passed. By this the whole army might readily have defiled through the South Mountains to fall on Lee's flank and rear.¹ If nothing had been accomplished by this means, the retreat of Lee would still have been followed so closely, that coming to the Potomac, and having an impassable river in his rear, his situation would have been one of the very gravest peril.

It cannot be said that General Meade was not alive to the importance of striking Lee a blow before he should be able to make good his retreat. But he was tardy in realizing the severity of the damage he had inflicted on his opponent, and the distance the army was compelled to march by the line adopted (double that by the Cumberland Valley), together with the slowness of the march (in part necessitated by the bad condition of the roads owing to the severe storm), resulted in Lee's being able to take up a position on the Potomac; and having reached this point three days before