Forget presidential or even 5th Amendment issues, can Mueller force Trump, or anyone, to say what they were thinking? Ask what I said or did, but I have an expectation of privacy when I think, and isn’t the left glad SCOTUS found that privacy right? Plead the 9th!
“..can Mueller force Trump, or anyone, to say what they were thinking?”
First, I would not talk to them under oath, there would be no cameras or stenographers, and every question would be answered “I don’t recall”.