After Antietam, the Army of the Potomac was given a new commander, Ambrose Burnside. Decisive in action but tactically inept, Burnside would offer Lee's army its most one-sided victory: at Fredericksburg.
On October 6, dismayed by McClellan's failure to follow Lee's army across the Potomac into Virginia, Lincoln had orders issued that directed him to “cross the Potomac and give battle to the enemy or drive him south.” Lincoln insisted, “Your army must move now while the roads are good.” Instead, McClellan sat back and watched as Stuart, following a suggestion from Lee, again encircled the motionless Army of the Potomac. On October 10, some 1,800 Confederate cavalry crossed the Potomac near Black Creek and moved on to Chambersburg, Pennsylvania. There Federal and state officials fled as the Confederates cut telegraph wires, seized horses, and destroyed any military equipment they couldn't carry away with them. They wrecked railroad equipment, including machine shops, depots, and several trains. Then they moved east through Emmitsburg, Maryland, on their way back to the Potomac, which they crossed on the 12th after a short skirmish near the mouth of the Monocacy in Maryland. They actually crossed at Poolesville, having pulled off another headlinegrabbing raid. In real military terms, however, the raid did little to the Union army, save again damage its pride.
Finally on October 16 the Union army probed Lee's forces, then in the Shenandoah Valley, with reconnaissances to Smithfield and Charles Town, in western Virginia. The bulk of the Army of the Potomac finally followed its reconnoitering cavalry, crossing the Potomac into Virginia on October 26, 20 days after Lincoln ordered the move. McClellan's troops marched east of the Blue Ridge, toward Warrenton. Lee, fearing that the Union commander could place his forces between him and Richmond, began moving to the south on October 28. On November 7, Lee wrote the secretary of war: “The enemy today occupied Warrenton, and his cavalry have reached the Rappahannock. The latter is reported