u.s. president donald trump plan invoke executive privilege way block former fbi director jam comey testify congress next week new york time say friday cite two unnamed senior administration officials saturday white house spokesperson refer question time story outside council outside council immediately respond request comment comey lead federal bureau investigation probe allege russian meddle last year u.s. presidential election possible collusion trump campaign president fire last month friday white house officials say know yet whether president donald trump would seek block comey testimony move could spark political backlash speak counsel yet know go respond white house spokesman sean spic tell reporters friday former fbi chief due testify thursday senate intelligence committee part russia-related investigation remark could cause problems republican president presidents assert executive privilege prevent government employees share information however legal experts say clear whether certain conversations trump comey president talk publicly would cover effort block comey private citizen testify could challenge court trump plan invoke executive privilege comey testimony ny time