If you want to destroy him, double-down on these delusions.

Why stop at Elvis? Get him talking about his theory on aliens, ask him to compare himself to Jesus and whether he'd do a better job of spreading Christianity than the big man himself, get him to discuss how to split Gaza to make everyone happy, ask how a successful coup of the whitehouse would look like, maybe even ask if Rosa Parks was being reasonable by not getting up out of her seat.

You don't destroy people like this by pointing out how stupid they are, because those die-hard followers will still worship him if he answers all the above. Where he'll be destroyed is in having those on the fence go from "he's a bit crazy, but he'll do something, so I'll vote for him" to "he's fucking nuts, he'll do something crazy, so I'll vote for Biden".