Here's a bit of his background.
The Observer: Judge Emmet G. Sullivan Slams Brakes on Another Prosecutorial Overreach
udge Sullivan gets it and his opinion, issued on Friday, begins with a bang: The governments power when prosecuting a criminal case is not infinite. Nor does it extend to any power not specifically forbidden by law. Comparing the governments baseless arguments to the conduct of a grade-schooler seeking to avoid detention, Judge Sullivan held: The government in this case has overstepped Rule 17.
He's needed where he is right now, but perhaps Trump can elevate him for seat number 5 or 6 in his second term.