"These cases concern the Tax Court's employment of special trial judges, auxiliary officers appointed by the Chief Judge of the Tax Court to assist in the work of the court. See 26 U.S.C. § 7443A(a). Unlike Tax Court judges, who are appointed by the President for 15-year terms, special trial judges have no fixed term of office. Any case before the Tax Court may be assigned to a special trial judge for hearing. Ultimate decision in cases involving tax deficiencies that exceed $50,000, however, is reserved for the Tax Court."