▁and ▁Iowa . ▁ ▁Le ad ership ▁ ▁Senate ▁ ▁President : ▁George ▁M . ▁Dallas ▁( D ) ▁ ▁President ▁pro ▁temp ore : ▁Will ie ▁P . ▁Mang um ▁( W ), ▁until ▁March ▁ 4 , ▁ 1 8 4 5 ▁ ▁Am bro se ▁H und ley ▁Se vier ▁( D ), ▁only ▁on ▁December ▁ 2 7 , ▁ 1 8 4 5 ▁ ▁David ▁R . ▁At ch ison ▁( D ), ▁from ▁August ▁ 8 , ▁ 1 8 4 6 ▁ ▁House ▁of ▁Representatives ▁ ▁Spe aker : ▁John ▁W . ▁Davis ▁( D ) ▁ ▁M embers ▁This ▁list ▁is ▁arranged ▁by ▁chamber , ▁then ▁by ▁state . ▁Sen ators ▁are ▁listed ▁by ▁class ▁and ▁Representatives ▁are ▁listed ▁by ▁district . ▁Sk ip ▁to ▁House ▁of ▁Representatives , ▁below ▁ ▁Senate ▁Sen ators ▁were ▁elected ▁by ▁the ▁state ▁legisl atures ▁every ▁two ▁years , ▁with ▁one - third ▁beginning ▁new ▁six - year ▁terms ▁with ▁each ▁Congress . ▁Pre ced ing ▁the ▁names ▁in ▁the ▁list ▁below ▁are ▁Senate ▁class ▁numbers , ▁which ▁indicate ▁the ▁cycle ▁of ▁their ▁election . ▁In ▁this ▁Congress , ▁Class ▁ 1 ▁meant ▁their ▁term ▁began ▁with ▁this ▁Congress , ▁facing ▁re - e lection ▁in ▁ 1 8 5 0 ; ▁Class ▁ 2 ▁meant ▁their ▁term ▁ended ▁with ▁this ▁Congress , ▁facing ▁re - e lection ▁in ▁ 1 8 4 6 ; ▁and ▁Class ▁ 3 ▁meant ▁their ▁term ▁began ▁in ▁the ▁last ▁Congress , ▁facing