washington senator john mccain chairman senate arm service committee say thursday may consider issue subpoena white house forthcoming detail ambush niger leave four u.s. soldier dead attack early month u.s. officials suspect carry local islamic state affiliate throw spotlight u.s. counter-terrorism mission west african country 800 u.s. troop may require subpoena mccain say ask step committee might need take determine happen four troop question information committee still need mccain say everything ask whether white house forthcoming information need committee add course not white house chief staff john kelly say pentagon investigation aim find happen niger investigation mean anything wrong investigation mean people head go roll fact need find happen happen say appearance white house brief room u.s. defense secretary jim mattis tell reporters thursday incident investigation defend military response even acknowledge yet accurate information incident initially pentagon announce three soldier kill ambush body fourth soldier sergeant la david t. johnson recover day late question raise take long u.s. military leave troop behind would ask question action troop catch firefight question whether everything could order bring everyone mattis say start meet israeli counterpart mccain say good conversation president donald trump national security adviser h.r mcmaster hop white house would eventually provide information need committee initial account 40-member patrol include dozen u.s. troop come swift attack militants rid dozen vehicles 20 motorcycle mission see relatively lower-risk endeavor america elite commandos arm air cover time could carry air strike necessary mattis say contact consider unlikely provide detail reason u.s. army soldier peace corps carry gun reality part danger troop face say heavy fire u.s. troop call french fighter jet air support firefight close quarter plan could engage instead leave circle overhead u.s. officials say french aircraft overhead within 30 minutes mattis say contract aircraft evacuate dead u.s. soldier johnson body find late local nationals u.s. military africa command say soldier area establish relations local leaders deem unlikely would meet resistance senator mccain say subpoena may require get answer niger ambush