Trump should address the nation. He should state that existing evidence already indicates that he was not involved in any illegal activity. Although he like to provide any further information to help resolve any remaining issues, the prosecutors behavior indicates his interest in an interview is solely to elicit some response that could be characterized as lying or perjury. Since he is not guilty of anything at this time, he cannot submit himself to a process whose sole intent is to trap him into illegal activity. If subpoenaed upon the advice of council he will assert his 5th amendment rights.
That is too complicated for 75% of voters to comprehend. Trump is a master of timing. He will expose the fraud investigation when it will be most beneficial.