Trump’s former White House Counsel Don McGahn reportedly stopped Trump from prosecuting Hillary Clinton and Jim Comey. Ari Melber breaks down how everything Don McGahn knows, Special Counsel Bob Mueller knows as well; McGahn is reportedly cooperating “extensively” with Mueller, sitting for at least 30 hours of interviews. Former House Judiciary Counsel Michael Conway, who wrote part of the Nixon impeachment recommendation tells Ari Melber that as a former White House counsel, McGahn will be Mueller’s “most important witness”.