In late August, two full corps of the Army of the Potomac (William B. Franklin's VI Corps and Edwin V. Sumner's II Corps) had arrived in Alexandria, but McClellan would not allow them to advance to Manassas because of what he considered inadequate artillery, cavalry, and transportation support.
I slutningen af august ankom to hele korps fra Army of the Potomac (William B. Franklin's VI Corps og Edwin V. Sumner's II Corps) til Alexandria i Virginia, men McClellan ville ikke lade dem rykke frem til Manassas, fordi han mente, at de ikke havde tilstrækkeligt artilleri, kavaleri og transportstøtte.