As Major General George B. McClellan was following the Confederate army in Maryland, he sent to Washington DC on September 10, 1862, that the Rebel forces numbered 120,000 soldiers. This was a gross error as Lee had less than 50,000 troops. McClellan's source of information on this was from a civilian observer.
When Confederate General Joseph Johnston withdrew his forces near Washington DC southwards to protect Richmond, one huge opportunity for General McClellan vanished. McClellan had hoped the Rebel army would remain north of Richmond. Had that happened two favorable elements of his campaign were ended. McClellan's plan was to have a chance to attack Johnston's forces from the rear and he also had the chance to place his army between the Rebel army and Richmond.
Allan Pinkerton was hired by US General George B. McClellan for espionage work for confederate operations.
General McClellan was pleased by the change of Confederate command due to the wounded General Johnston. McClellan considered Lee to be meek and clearly was not chosen to lead any major Southern armies. Also, McClellan had a brief encounter with some of Lee's soldiers who failed to retain what would become West Virginia.
Confederate General Robert E, Lee and Union General George McClellan
general Robert E. Lee
The semi-blockade of the lower Potomac River set by Confederate artillery banks seemed to elude McClellan's attention. This problem was basically solved when Confederate General Longstreet, abandoned the "blockade" as he was sure he would not be able to sustain it.
George b McClellan was a Union general. All the generals do is command their troops.
Captain George Custer was on a scouting mission for General George B. McClellan on September 15, 1862. He reported to the general that he had observed the Confederate army in full view and in perfect line, established on a ridge near Sharpsburg. Custer noted that the Rebel battle line was one and a half miles long and that Confederate General Longstreet had forty cannons.
Confederate General led the Confederate army at the Battle of Antietam in September of 1862. Lee lost the battle and had to retreat back to Virginia. Union General George B. McClellan led the Union army to the victory.
Richmond, Virginia
McClellan's Peninsular campaign failed because the Confederate army was defending Richmond better that McClellan anticipated. They retreated, then turned and attacked McClellan, surprising the Union general.
Apparently, General McClellan's warning to General in Chief Winfield Scott went unheeded. In September of 1861, the US Secretary of War, Simon Cameron received in writing McClellan's alarming news that the Rebel army was, as of September 13, 1861, probably 170,000 men strong. McClellan voiced concern that at most, he could muster between 60,000 to 80,000 troops.In actuality, the Confederate force on the south side of the Potomac River was about 45,000 men. And, no plans were made by Jefferson Davis or General Joseph Johnston to assault Washington DC.