The former Fox News host made the eyebrow-raising comment to ex-Trump official Mick Mulvaney. Bill O’Reilly called Stephen Miller the “most powerful guy in the White House right now” in a conversation with former Trump official Mick Mulvaney . (Watch the video below.) Miller, the White House deputy chief of staff, is often credited as the architect of Trump’s immigration policy that again received a stinging rebuke (along with the war against Iran) at the “No Kings” rallies last weekend.