                     United States Court of Appeals
                            FOR THE EIGHTH CIRCUIT
                                    ___________

                                    No. 99-3538
                                    ___________

United States of America,                *
                                         *
             Appellee,                   *
                                         * Appeal from the United States
      v.                                 * District Court for the
                                         * District of Nebraska.
Patricia Tew,                            *
                                         *      [UNPUBLISHED]
             Appellant.                  *
                                    ___________

                            Submitted: March 6, 2000
                                Filed: March 14, 2000
                                    ___________

Before LOKEN, FAGG, and HANSEN, Circuit Judges.
                           ___________

PER CURIAM.

       Patricia Tew pleaded guilty to conspiring to distribute methamphetamine in
violation of 21 U.S.C. § 846. Following an evidentiary sentencing hearing, the district
court1 sentenced Tew to 151 months in prison and five years supervised release, based
upon its drug quantity finding that she was responsible for distributing more than two
kilograms of methamphetamine. On appeal, Tew argues this drug-quantity finding was
clearly erroneous. We reject this contention because the finding was based upon the


      1
        The HONORABLE RICHARD G. KOPF, United States District Judge for the
District of Nebraska.
testimony of two witnesses, and the district court’s witness credibility findings are
virtually unreviewable on appeal. See United States v. Johnson, 169 F.3d 1092, 1098
(8th Cir.), cert. denied, 120 S. Ct. 143 (1999).

       Tew next argues the government impermissibly refused to file a substantial-
assistance motion because of her gender or national origin. This argument was not
raised in the district court, and in any event Tew has failed to make a substantial
threshold showing of an unconstitutional motive. See Wade v. United States, 504 U.S.
181, 186 (1992); United States v. Wilkerson, 179 F.3d 1083, 1086 (8th Cir. 1999).
Finally, Tew argues the United States Sentencing Commission violates the
constitutional separation of powers doctrine, an argument foreclosed by Mistretta v.
United States, 488 U.S. 361, 412 (1989).

      The judgment of the district court is affirmed.

      A true copy.

             Attest:

                     CLERK, U. S. COURT OF APPEALS, EIGHTH CIRCUIT.




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