washington bipartisan group dozens former u.s. homeland security officials send letter support nomination kirstjen nielsen new head department ahead confirmation hear wednesday senate homeland security committee among signers former homeland security dhs secretaries tom ridge michael chertoff republicans serve former president george w. bush ms nielson engage counter-terrorism all-hazard risk mitigation critical infrastructure protection response policy early days know homeland security two former secretaries write latter view reuters separate letter sign former national security agency director keith alexander former dhs officials charles e. allen jam m. loy john mclaughlin letter also sign jane holl lute alejandro mayorkas serve secretaries dhs former president barack obama 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 work include service department transportation security administration former republican president george w. bush white house homeland security council nominate role john kelly previous secretary name white house chief staff summer nielson work kelly deputy white house prior nominate october former u.s. homeland security officials back nominee ahead hear