After months of preparation (along with criticism for the inaction of The Army of the Potomac), McClellan himself departed Washington (“that sink of iniquity”) on this date 150 years ago today. Aboard the Commodore, the destination was Fortress Monroe and ultimately a conquest of Richmond through the Peninsula Campaign.
President Lincoln did not see this as the preferred plan of operation, but he had agreed – provided that Washington was sufficiently protected. “Sufficiently” … what did that mean specifically in terms of total numbers of troops? McClellan and Lincoln had variant definitions.
For McClellan, he saw little threat to the city. Therefore, in his view, his cursory accounting of local troops not committed to the peninsula campaign revealed numbers more than sufficient. The General’s listing did not sit well with Lincoln and Stanton, as McClellan had even tallied Banks’ 30,000 troops at Harpers Ferry among the total.
For Lincoln, the threat to the capital was very real – especially in the wake of events at Winchester on March 23rd (see blog posting of 3/23/12). Though history supports McClellan’s view as more accurate, the loss of Washington would be to lose everything and was therefore entirely an insufferable potentiality to not be considered lightly.
Over the coming hours, as Lincoln and Stanton gained a more precise understanding of the accounting of troops designated by McClellan for the defense of the city, the decision was made to withhold McDowell’s Corps of 30,000 troops.

Fort Monroe today as seen from the air - the star-shaped area in the center is the Civil War era fortress.
McClellan’s reaction to this event was entirely predictable, writing to his wife that “history will present a sad record of these traitors who are willing to sacrifice the country & its army for personal spite.”
The movement of the army to the peninsula was hardly a surprise to the Confederates. The Springfield (Massachusetts) Daily Republican wrote at this time: “The latest accounts from Richmond show that the Rebels are crowding troops down upon the York and James River, showing they know where to expect Gen. McClellan.”
But whatever, the Army of the Potomac was on the move, and for this Lincoln was pleased, along with the country and their hopes for success.