because he lacks the cover up network of powerful government people
.
So too, apparently, Manafort, Cohen, Flynn and Stone lack 'the cover up network'.
Nixon and Reagan lacked it too, but not in the end the pardon power from others to get Nixon off the hook and enable Reagan's Iran-Contra felons to secure get out of jail free cards.
Gotta admire the law and order GOP for regularly educating us on how it's supposed to work, pardons aside.