I wish President Trump would stop stalling....he is making the investigation go longer, it was JANUARY when he was first suppose to be interviewed for goodness sake.... and he has dragged this out in his Reality TV production of will he or will he not.... and purposely stalling for his own evil genius reasons, like needing the 6 months to convince his supporters that this is all a witch hunt campaign that he has promoted since then.........so they won't think anything is wrong about him refusing to testify.
I agree with Old School, I would through my body in front of him to prevent him from testifying because he doesn't have any kind of relationship with telling truth over fiction....if I were his lawyer....
but if he were to refuse the interview, depending on what Mueller needed to ask him questions about and the necessity to speak with Trump.... the grand jury could subpoena him, and then Trump might refuse, and then this becomes a battle that goes to the supreme court to decide, whether a President of the US, is ABOVE the Law and can rule with lawlessness.... and Trump loves the fight, he lives for it, so you know this will be years in court.... regardless of it tearing our Nation apart!