The U.S. Supreme Court should not disturb a federal appeals court’s appointment of a special prosecutor who will defend the criminal contempt order lodged against President Donald Trump ally and former Arizona Sheriff Joe Arpaio, the Justice Department said in a new court filing.

The special prosecutor, Christopher Caldwell of Boies Schiller Flexner, was appointed by the U.S. Court of Appeals for the Ninth Circuit last year. The appointment came after the Justice Department announced it would back Arpaio’s push to vacate his contempt conviction after he received a pardon from Trump.