A real witch hunt is an inquisition into doctrinal apostasy, especially that which results in curses, plagues, inflictions, crop failures and any otherwise unexplainable misfortunes. In modern times it's equivalent to a fishing expedition, an attempt to find something unspecified. Robert Mueller's investigation is neither, it is focused on proving or disproving collusion, obstruction of justice, and acceptance of emoluments by Trump or his associates. There is ample reason to suspect that any of those things MIGHT have happened, hence the investigation. If as I suspect, Trump isn't seriously involved in many, most, or all of those things, then the investigation will vindicate him, just as James Comey's FBI investigation vindicated Hillary Clinton of specific indictable offenses.

Trump, who usually enjoys the spotlight on him, doesn't welcome this attention. He should welcome this as a chance to prove his innocence, and if I were he, I would smile and tell the public exactly that.