of bold attacks: the Seven Days Battles. Despite superior Union numbers and some clumsy tactical performances by his subordinates, Lee's attacks derailed McClellan's plans and drove back most of his forces. Confederate casualties were heavy, but an unnerved McClellan, famed for his caution, retreated to the lower James River, and abandoned the Peninsula completely in August. This success changed Confederate morale and the public's regard for Lee. After the Seven Days Battles, and until the end of the war, his men called him “Marse Robert", a term of respect and affection. The setback, and the resulting drop in Union morale, impelled Lincoln to adopt a new policy of relentless, committed warfare. After the Seven Days, Lincoln decided he had to move to emancipate most Confederate slaves by executive order, as a military act, using his authority as commander-in-chief. To make this possible, he needed a Union victory. Wheeling to the north, Lee marched rapidly towards Washington, D.C. and defeated another Union army under Gen. John Pope at the Second Battle of Bull Run in late August. He eliminated Pope before reinforcements from McClellan arrived, knocking out an entire field command before another could arrive to support it. In less than 90 days, Lee had run McClellan off the Peninsula, defeated Pope, and moved the battle lines north, from north of Richmond to south of Washington. Lee chose to take the battle off southern ground and invaded Maryland and Pennsylvania, hoping to collect supplies in Union territory, and possibly win a victory that would sway the upcoming Union elections in favor of ending the war. This was sent amiss when McClellan's men found a lost Confederate dispatch, Special Order 191, revealing Lee's plans and movements. McClellan always exaggerated Lee's numerical strength, but now he knew the Confederate army was divided and could be destroyed in detail. Still, in a characteristic manner, McClellan moved slowly; he failed to realize a spy had informed Lee that he possessed the plans. Lee quickly concentrated his forces west of Antietam Creek, near Sharpsburg, Maryland, where McClellan attacked on September 17. The Battle of Antietam was the single bloodiest day of the war, with both sides suffering enormous losses. Lee's army barely withstood the Union assaults, and retreated to Virginia the next day. The narrow Confederate defeat gave President Abraham Lincoln the opportunity to issue his Emancipation Proclamation, which put the Confederacy on the diplomatic and