washington president donald trump nominate kirstjen nielsen top aide white house chief staff seek instill order trump team lead u.s. department homeland security white house say statement wednesday confirm senate nielsen would take rein sprawl department 240,000 employees responsible u.s. border airport security immigration policy disaster response refugee admissions matter nielsen 45 cyber security expert considerable resume homeland security include work department transportation security administration former republican president george w. bush white house homeland security council nielsen retire marine corps general john kelly chief staff secretary homeland security open months trump presidency kelly bring white house deputy trump name chief staff july replace reince priebus six months job nomination require senate confirmation nielsen departure white house would mark late upheaval trump white house team responsible carry kelly order get access president result irritate white house officials limit contact trump accord source familiar situation kelly seek bring order chaotic west wing since replace priebus trump welcome change extent although privately confide friends limitations access oval office sometimes go far put nielsen homeland security post allow trump kelly keep close eye department get white house could permit kelly strictness relax department lead act secretary elaine duke since kelly take white house post cyber security one primary issue homeland security department portfolio nielsen previously work cyber think tank george washington university block white house consider well-versed technical missions department share cyber-threat information private sector department create sept. 11 2001 attack unite state expose crack country homeland security apparatus appointment come busy time department one agencies federal emergency management agency oversee disaster relief hurricane-hit puerto rico texas florida well wildfire-ravaged areas california department also responsible u.s. border security department major player implement trump aggressive stance toward deport illegal immigrants well vet low number refugees trump decide allow unite state devise travel ban six muslim-majority nations north korea certain venezuelans low-drama pick seem like low-drama pick little concern seem little background immigration security policy individual agencies good hand already strong core career managers say jessica vaughan director policy study center immigration study favor limit immigration nielsen know hard-line view immigration like white house adviser stephen miller confirm nielsen would first homeland security secretary previously serve rank-and-file member department previous dhs secretaries criticize possess enough technical fluency address cyber threats face nation also serve corporate attorney congressional staff member white house statement say kirstjen policy wonk heart especially come cyber frank cilluffo former senior homeland security official bush work nielsen george washington university nielsen would immediately give task help coordinate federal response potential cyber attack target elections u.s. intelligence agencies conclude russia meddle 2016 presidential election try help trump win part hack release email embarrass democratic opponent hillary clinton online propaganda russia deny meddle election trump deny collusion campaign moscow jeh johnson serve former democratic president barack obama last homeland secretary chief designate election systems critical infrastructure widen support department provide state department clash several state officials best cooperate defend future elections politico first report appointment trump nominate white house aide homeland security post