In my opinion the whole battle was Strategical mistake. Lee´s and Longstreets original plan was to march toward Washington and force the Union troops to attack them so they could fight a defensive battle in offensive campaign since they were outnumbered.
No matter, first the Confederate cavalry failed miserable in scouting the Union force and after that the lead Column of Confederate army was sucked in the battle becouse they really were not aware what they were up against when they first engaged Bufords cavalry.
After the first days events and the arrival of the main force of Union army the battle was practicly lost. At this point Lee made the final mistake to fight there,while Longstreet opposed Lee´s decision vigorously.