A telling example of his lack of control was during the Northern Virginia Campaign of 1862, when Halleck was unable to motivate McClellan to reinforce Pope in a timely manner, contributing to the Union defeat at the Second Battle of Bull Run.
Et godt eksempel på hans manglende kontrol så man under kampagnen i det nordlige Virginia i 1862, hvor Halleck ikke kunne få McClellan til at sende forstærkninger til John Pope i tide, hvilket bidrog til Unionens nederlag i det Andet slag ved Bull Run.