Earlier quoted context omitted.
He was pretty explicit about the reason why. He feared Trump would force the DOJ to prosecute them. And, based on what Trump's done so far with the DOJ and his enemies, he was right to do so.
"My president is right to pardon whoever it likes, but not your president.. " I think this whole pardoning thing should go away. It makes the presidents Kings.
If the goal of the pardon was to handle a corrupt Judicial branch, then a better answer would have been for the Executive branch to nominate someone for a pardon to the Legislative and require a 2/3 majority of the Legislative to approve.
But something like that would fly in the face of the "Unitary Executive" insanity and would (I suspect) require a constitutional amendment, which is no longer remotely feasible.