In United States v. Presser, 844 F.2d 1275, 1279 (6th Cir. 1988), the district court issued a discovery order requiring the government's immediate disclosure of impeachment evidence "which tends to negate guilt." The government refused to disclose "government evidence which could impeach defense witnesses." Id. at 1278. The appellate court found that "neither case, however, gives the defense a general right to pre-trial discovery of evidence impeaching defense witnesses, where the prosecution denies that any such material is exculpatory and material under Brady." Id. at 1283. Furthermore, the court concluded that "the government need not disclose impeaching material in its possession relating to any potential defense witness where that impeaching material does not meet the Brady test of being material and exculpatory." Id. at 1285. "Evidence is material only if there is a reasonable probability that, had the evidence been disclosed to the defense, the result of the proceeding would have been different. A 'reasonable probability' is probability sufficient to undermine confidence in the outcome." Id. at 1281.