Ka cika wannan jumla: A shekara ta 1855, Brainerd yana ɗaya daga cikin waɗanda suka kafa sabuwar jam'iyyar Republican, wadda aka kafa a matsayin babbar ƙungiyar siyasa ta ƙasar da ke yaƙi da bautar. Ya yi aiki a matsayin shugaban farko na Jam'iyyar Republican na Vermont, kuma yana ɗaya daga cikin shugabannin jam'iyyar jam'iyyar biyar waɗanda suka ba da kira ga na farko
Taron kasa na Jamhuriyar Republican a shekara ta 1856. Brainerd wakili ne, kuma a matsayin shugaban wucin gadi ya kira taron zuwa tsari don zamansa na farko. Daga baya aka zabi Brainerd ya zama daya daga cikin mataimakan shugaban majalisa, kuma an nada shi a matsayin memba na Kwamitin Kasa na Republican. An zabi Brainerd a matsayin daya daga cikin masu zaben shugaban kasa na Vermont bayan zaben 1856. Lokacin da masu zaben Vermont suka hadu a watan Disamba don jefa kuri'unsu, an zabi Brainerd a matsayin shugaban su. Dukkansu sun zabi tikitin Jam'iyyar Republican na John C. Frémont don shugaban kasa da William L. Dayton don mataimakin shugaban kasa, wanda ya dauki Vermont amma ya rasa zaben.