United States Court of Appeals
                            FOR THE EIGHTH CIRCUIT
                                     ___________

                                     No. 10-3118
                                     ___________

Roberto Sanchez-Florez,                   *
                                          *
             Appellant,                   *
                                          * Appeal from the United States
      v.                                  * District Court for the
                                          * Northern District of Iowa.
United States of America,                 *
                                          * [UNPUBLISHED]
             Appellee.                    *
                                     ___________

                              Submitted: June 24, 2011
                                 Filed: June 29, 2011
                                  ___________

Before WOLLMAN, BOWMAN, and SMITH, Circuit Judges.
                        ___________

PER CURIAM.

       Roberto Sanchez-Florez was convicted by a jury of conspiracy to distribute 500
grams or more of a methamphetamine mixture. See United States v. Sanchez-Florez,

(8th Cir. 2008) (affirming on direct appeal). He now appeals the district
court’s1 judgment dismissing his 28 U.S.C. § 2255 motion, and has been granted by
the district court a certificate of appealability (COA) on his claims of ineffective
assistance of trial and appellate counsel. Following careful review, see Covey v.
United States, 

, 906 (8th Cir. 2004) (district court’s denial of ineffective-

      1
      The Honorable Donald E. O’Brien, United States District Judge for the
Northern District of Iowa.
assistance claim presents mixed question of law and fact; ineffective-assistance issue
is reviewed de novo, but findings of underlying predicate facts are reviewed for clear
error), we agree with the district court that Sanchez-Florez did not show that he
suffered prejudice as a result of deficient performance by his trial or appellate counsel,
most notably with regard to counsel’s efforts to impeach witnesses, see United States
v. Orr, 

, 951-52 (8th Cir. 2011) (failure to impeach witness constitutes
ineffective assistance when there is a reasonable probability that, absent counsel’s
failure, jury would have had reasonable doubt of defendant’s guilt); Sinisterra v.
United States, 

, 912 (8th Cir. 2010) (claim that appellate counsel was
ineffective for failing to raise issue on appeal failed without showing of prejudice);
see also 

(noting overwhelming evidence of
defendant’s guilt); Williams v. United States, 

, 1013 (8th Cir. 2006)
(when determining if prejudicial deficient performance by counsel exists, court must
consider totality of evidence before judge or jury).

       We also decline to expand the scope of the COA to reach additional arguments
in Sanchez-Florez’s supplemental brief that he was denied due process by the trial
court’s admission of noncredible witness testimony, see Winfield v. Roper, 

, 1040 (8th Cir. 2006) (grant of COA requires demonstration that reasonable
jurist would find district court’s ruling on constitutional claim debatable or wrong),
and we grant counsel’s motion to withdraw.

      The judgment is affirmed.
                      ______________________________




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