I think Trump should ambush Mueller by having him come to the White House for their meeting. Have the meeting in the oval office (power of the presidency) and when Mueller sits down have Fox News bring in live cameras and broadcast on live TV. Then Trump should ask Mueller if he found any collusion with Russia forcing him to answer. Then ask him what crime was committed to to justify the investigation. After he answers then Trump should accuse him of a witch hunt.
Trump should not answer any questions, if Mueller walks out it will prove it is a witch hunt.
Just my opinion.