I think "the opinion" that the FBI is not supposed to investigate a possible crime is actually a delusion. We have loads of Trump's "opinions" actually being delusions, right from the size of his inauguration crowd.

Quote
“I believe that they fit the pattern of delusions rather than just plain lies,” she continued, pointing to the claim he made during a meeting with Jens Stolenberg, Nato’s secretary-general, that “many legal scholars” were “looking at the transcripts” of his 25 July phone call with Ukrainian president Volodymyr Zelenskyy and agreeing with his description of the call as “absolutely perfect” as an example of his pathology.

That's not an opinion, it's a delusion. He pulled that right out of his ass, and now he believes it.