“Imagine an incoming president of the United States announcing that he or she would take advice on criminal justice matters exclusively from a Federal Defender’s office. Moreover, the new chief executive intends to put the defenders in charge of federal prisons, forensic science, and the clemency process. After all, the president might argue, the defenders understand federal criminal law from the ground up, have a rich understanding of the social conditions that lead to criminal behavior, and are the federal attorneys most responsible for ensuring individual Constitutional protections.”