The condition was this. The retention of McDowell's corps before Washington published the anxiety of the administration. The Confederate advantage lay in keeping that anxiety alive and continuing to neutralize that large body of troops. Strategists far less able than the Southern generals could not have missed so obvious a point, neither could they have missed the equally obvious means at their disposal for achieving these purposes. At the upper end of the valley of the Shenandoah Stonewall Jackson had an army, raised by recent accretions to nearly or quite 15,000 men. The Northern generals erelong learned to prognosticate Jackson's movements by the simple rule that at the time when he was least expected, and at the place where he was least wanted, he was sure to turn up.[17] The suddenness and speed with which he could move a body of troops seemed marvelous to ordinary men. His business now was to make a vigorous dashing foray down the valley. To the westward, Fremont lay in the mountains, with an army which checked no enemy and for the existence of which in that place no reasonable explanation could be given. In front was Banks, with a force lately reduced to about 5,000 men. May 14, Banks prudently fell back and took position in Strasburg.[18] Suddenly, on May 23, Jackson appeared at Front Royal; on the next day he attacked Banks at Winchester, and of course defeated him; on the 25th Banks made a rapid retreat to the Potomac, and Jackson made an equally rapid pursuit to Halltown, within two miles of Harper's Ferry. The news of this startling foray threw the civilians of Washington into a genuine panic, by which Mr. Lincoln was, at least for a few hours, not altogether unaffected.[19] Yet, though startled and alarmed, he showed the excellent quality of promptitude in decision and action; and truly it was hard fortune that his decision and his action were both for the worst. He at once ordered McDowell to move 20,000 troops into the Shenandoah Valley, and instructed Fremont also to move his force rapidly into the valley, with the design that the two should thus catch Jackson in what Mr. Lincoln described as a "trap."[20] McDowell was dismayed at such an order. He saw, what every man having any military knowledge at once recognized with entire certainty, and what every military writer has since corroborated, that the movement of Jackson had no value except as a diversion, that it threatened no serious danger, and that to call off McDowell's corps from marching to join McClellan in order to send it against Jackson was to do exactly that thing which the Confederates desired to have done, though they could hardly have been sanguine enough to expect it. It was swallowing a bait so plain that it might almost be said to be labeled. For a general to come under the suspicion of not seeing through such a ruse was humiliating. In vain McDowell explained, protested, and entreated with the utmost vehemence and insistence. When Mr. Lincoln had made up his mind, no man could change it, and here, as ill fortune would have it, he had made it up. So, with a heavy heart, the reluctant McDowell set forth on his foolish errand, and Fremont likewise came upon his,--though it is true that he was better employed thus than in doing nothing,--and Jackson, highly pleased, and calculating his time to a nicety, on May 31 slipped rapidly between the two Union generals,--the closing jaws of Mr. Lincoln's "trap,"--and left them to close upon nothing.[21] Then he led his pursuers a fruitless chase towards the head of the valley, continuing to neutralize a force many times larger than his own, and which could and ought to have been at this very time doing fatal work against the Confederacy. Presumably he had saved Richmond, and therewith also, not impossibly, the chief army of the South. The chagrin of the Union commanders, who had in vain explained the situation with entire accuracy, taxes the imagination.