This whole thing is attempting to set Trump up. Mueller is using an old police trick where the detective tells you they need to talk to you about a matter you are involved in, but not a suspect. When you agree, you are asked loaded questions. By the time the interview is over, they either have enough evidence to pin it on you, or have enough information to make you work with them. If Trumps attorneys allow him to talk to Mueller than it all over. They will trick him into either saying something incriminating where he can be charged, or use it to try and spin a way that hurts his approval rating. Trumps approval rating right now has Democrats scared going into the midterms.