“I have no recollection.......
This is legalese for “I’m lying to you right now but I won’t admit it, so my attorney advised me to say “I can’t remember”.
He’s a f’n LIAR.
There are other possibilities - he is lying because he and his minions have destroyed all their incriminating emails and memos, so he has nothing to fear about lying.
Or, he has a brain tumor which causes selective amnesia on all subjects related to Mexico and guns.