Okay, you had a security clearance, and you signed an NDA saying that you won't talk about anything you know, even now. That basically means that you no longer have a security clearance, and that even though you might still know some classified material, it's not allowed for you to talk about it. If for some reason, they needed you to talk about what you know, you would be "read in", and given a temporary clearance so that you could go to whatever meeting to talk about what you still know. Same thing with Trump. He's no longer president, so he no longer has a security clearance, and would have signed an NDA saying that he wouldn't talk about any classified material that he knows. If he (or you) were caught talking about classified material, the NDA that was signed would open you and him up to severe punishments for disclosing classified information. Go ahead, try to tell us all how people can get security clearances for life again because of knowing something classified. The NDA stops that. And, if you went back to where you worked at previously and asked to see classified information that you had previously had access to, they would politely tell you to fuck off.