Instead of striking at a vulnerable point he sat down in a methodical fashion to besiege Yorktown. While he was waiting for the reinforcements he had demanded, the garrison got away as Johnstone had done from before Manassas, and an attempt to push forward resulted in the defeat of his lieutenant, Hooker, at Williamsburg. McDowell, who was at Fredericksburg, was ordered to join and reinforce McClellan, but the junction was never made, for at the moment Jackson took the field and effected one of the most brilliant exploits of the war. The Union troops in the Shenandoah Valley were much more numerous than the force which Jackson had at his disposal, but they were scattered at various points, and by a series of incalculably rapid movements the Southern captain attacked and overwhelmed each in turn. The alarm at Washington was great, and McDowell hastened to cut him off, only to discover that Jackson had slipped past him and was back in his own country. Meanwhile McClellan, left without the reinforcements he had expected, was attacked by Lee and beaten back in seven days' consecutive fighting right to Harrison's Landing, where he could only entrench himself and stand on the defensive. Richmond was as far off as ever. One piece of good news, however, reached Washington at about this time, and once again it came from the West. Towards the end of April Farragut, the American admiral, captured the city of New Orleans. The event was justly thought to be of great importance, for Grant already dominated the Upper Mississippi, and if he could join hands with a Union force operating from the mouth of the great river, the Confederacy would be cut in two. Perhaps the contrast between the good fortune which had attended the Federal arms in the West and the failure of the campaign in Eastern Virginia was responsible for the appointment of a general taken from the Western theatre of war to command the army of the Potomac. Lincoln, having supported McClellan as long as he could, was now obliged to abandon his cause, and General Pope was appointed to supreme command of the campaign in Eastern Virginia. The change brought no better fortune; indeed, it was the prelude to a disaster worse than any that McClellan had suffered. Pope advanced by the route of the original invasion, and reached exactly the point where McDowell's army had been routed. Here he paused and waited. While he lay there Jackson made another of his daring raids, got between him and Washington and cut his communications, while Lee fell upon him and utterly destroyed his army in the second battle of Bull Run.