Comey was fired for being corrupt, and going easy on Hillary. Trump may bring that up to the press, but no way is he going to officially claim he wants that same biased treatment. Get real. And Trump may hold all the wild cards and this may completely blow over. But a special counsel investigating the President is the singular most dangerous legal threat to a sitting President. And any claims that Mueller or the FBI is corrupt don’t mean jack until a few of them start getting arrested.
Politically, the open corruption of the FBI senior leaders who have been the engine of the investigation is what makes it possible for Trump to not grant an interview.
Star was an actual prosecutor under the old law. (still dubious) After Clinton, that law was changed and Mueller does not have his powers.
All Trump needs is backing of the GOP congress and he can ignore Mueller’s request. That has been growing in the recent weeks as GOP leaders are turning on the FBI, the Mueller team, and calling for it to be terminated. Bannon was flushed which also made the GOP happy. Tax cuts made them happy.
The politics are on Trumps side and the coup is on the run. Next the IG report will come in.
Not testifying will show their weakness and fatally wound the Mueller team.