▁defense , ▁and ▁destroy ▁the ▁Union ▁Army ▁of ▁the ▁C umber land . ▁If ▁a ▁major ▁victory ▁er asing ▁the ▁Union ▁g ains ▁of ▁the ▁Tul lahoma ▁Camp aign ▁and ▁a ▁winning ▁of ▁the ▁strateg ic ▁initi ative ▁could ▁be ▁achieved ▁in ▁late ▁ 1 8 6 3 , ▁any ▁threat ▁to ▁Atlanta ▁would ▁be ▁elimin ated ▁for ▁the ▁near ▁future . ▁Even ▁more ▁significantly , ▁a ▁major ▁military ▁revers al ▁going ▁into ▁the ▁election ▁year ▁of ▁ 1 8 6 4 ▁could ▁have ▁sever ely ▁har med ▁President ▁Lincoln ' s ▁re - e lection ▁ch ances , ▁caused ▁the ▁possible ▁election ▁of ▁Dem ocrat ▁nom ine e ▁George ▁B . ▁McC le ll an ▁as ▁president , ▁and ▁the ▁c ess ation ▁of ▁the ▁Union ▁war ▁effort ▁to ▁sub due ▁the ▁South . ▁ ▁Sub sequ ent ▁events ▁The ▁Ch ick am aug a ▁Camp aign ▁was ▁followed ▁by ▁the ▁Batt les ▁for ▁Ch att ano oga , ▁sometimes ▁called ▁the ▁Ch att ano oga ▁Camp aign , ▁including ▁the ▁re open ing ▁of ▁supply ▁lines ▁and ▁the ▁Batt les ▁of ▁Look out ▁Mountain ▁( Nov ember ▁ 2 3 ) ▁and ▁Mission ary ▁R idge , ▁( Nov ember ▁ 2 5 ). ▁Rel ief ▁forces ▁commanded ▁by ▁Maj . ▁Gen . ▁U ly ss es ▁S . ▁Grant ▁broke ▁B rag g ' s ▁g rip ▁on ▁the ▁city , ▁sent ▁the ▁Army ▁of ▁Tennessee ▁into ▁retre at , ▁and ▁opened ▁the ▁gateway ▁to ▁the ▁Deep ▁South ▁for ▁Maj