republican vice presidential candidate mike pence say sunday evidence implicate russia recent email hack tie nov. u.s. election contradict run mate donald trump cast doubt russia involvement pence comment come u.s. vice president joe biden say interview air sunday unite state would send message russia time choose email attack obama administration officials initially refuse say think russia behind attack accuse moscow first time early month president barack obama say interview nbc news anything possible ask russia hack democratic national committee know russians hack systems government systems private systems obama say motives term leak say directly know donald trump repeatedly express admiration vladimir putin director national intelligence jam clapper speak hack dnc email say u.s. intelligence community ready make call attribution responsible homeland security secretary jeh johnson offer state officials help hack threats possible election tamper face unsubstantiated allegations trump system open fraud speak conference washington clapper say russians hack systems time officially blame intrusions democratic party organizations live interview washington post clapper say russia tradition try interfere elections countries add big concern foreign power would try affect outcome u.s. election instead cast doubt whole process u.s. government first time formally accuse russia campaign cyber attack democratic party organizations believe base scope sensitivity efforts russia senior-most officials could authorize activities obama administration say statement biden say interview nbc news unite state would send proportional response russia hack time choose circumstances great impact u.s. officials step rhetoric russia link email hack