After Hunter's retreat from the Shenandoah, Confederate Lieutenant General Jubal Early rushed north with his Army of the Valley up the Shenandoah, invaded Maryland, and threatened Washington, D.C. Sheridan was determined to wipe out Early's forces, but he needed to move cautiously so that no major defeat would occur that might imperil the re-election of President Abraham Lincoln in November. What is known as the Valley Campaign opened on August 16 in the Battle of Guard Hill, when Union forces surprised Confederate cavalry riding to reinforce Early in Maryland. Early won the initial skirmishes, but Sheridan's forces began pushing south down the Shenandoah Valley again. Early dispersed his forces to continue raiding the B&O Railroad, hoping Sheridan would follow. But Sheridan instead struck at Winchester, Virginia. In the Battle of Opequon on September 19, 1864, Meigs was again in combat. The battle was a decisive victory for the Army of the Shenandoah, and Early took ruinous casualties. Sheridan promoted Meigs to brevet Captain the following day for his battlefield valor.