When special counsels or FBI agents ask questions of one of these powerful people, they are not fact-finding. They’ve already done their homework. They’ve already gathered facts—almost certainly many more facts than the interviewee knows. They are asking questions the answers to which they can already prove, hoping that the interviewee will tell a provable lie, and thus commit a crime, or at least lock themselves into a feckless story that ties their hands later. The law that makes it a crime to lie to federal investigators does not require the lie to fool the investigators for a nanosecond. A lie must be “material” to be criminal, but that only means that the lie is the kind of statement that could conceivably influence the government, not one that actually did. The FBI can roll up with irrefutable proof of something, ask the target a question hoping for a lie, collect the lie they wanted, and reap a felony conviction.
Some people say, “Well, there’s an easy solution—just tell the truth.” Casual acquaintance with President Trump suggests that’s not an easy solution to him. I’m not saying that he constantly lies consciously and deliberately, but he certainly says untrue things constantly and gratuitously, in the way that characters on Deadwood swear. There’s little reason to think he can learn to change for an interview, particularly one with a nemesis who infuriates him.
Anyway, even an honest, circumspect person faces grave peril in such an interview. FBI agents and prosecutors are adept at putting interviewees ill at ease. The pressure is immense. Human memory is fallible, and the interrogators are not disposed to view misremembered statements as accidents.