Arpaio, who is now 85, is scheduled to be sentenced on 5 October for his criminal contempt conviction by a judge on 31 July.  However, he plans to appeal the conviction and get a trial by jury.  It would be best for Trump to hold off doing anything while the appeal plays out.  If the appeal is approved and Arpaio is found not guilty by a jury, end of situation.  If the appeal is denied and Arpaio is subsequently sentenced or if he is found guilty by a jury, Trump could then decide whether to commute the sentence, as President Bush did for Scooter Libby, or pardon Arpaio.