 Back in Washington , a reorganization of units created the Army of Virginia under Maj. Gen. John Pope , who was directed to advance toward Richmond from the northeast . McClellan resisted calls to reinforce Pope 's army and delayed return of the Army of the Potomac from the Peninsula enough so that the reinforcements arrived while the Northern Virginia Campaign was already underway . He wrote to his wife before the battle , " Pope will be thrashed ... & be disposed of [ by Lee ] . ... Such a villain as he is ought to bring defeat upon any cause that employs him . " Lee had assessed McClellan 's defensive nature and gambled on removing significant units from the Peninsula to attack Pope , who was beaten decisively at Second Bull Run in August . 
