Impeachment evidence is offered to discredit a witness [and] reduce the effectiveness of their testimony by bringing forth evidence which explains why the jury should not put faith in their testimony.
Impeachment by contradiction is evidence used to attack the credibility of witnesses by the presentation of evidence showing that facts asserted or relied upon in their testimony are false. Wegener v. Johnson, 527 F. 3d 687, 691 (8th Cir. 2008).
Separate and apart from whether the impeachment evidence contradicts a witness’ testimony, there are occasions where impeachment evidence also tends to establish the truth of a necessary fact or issue. Whether impeachment evidence provides some utility beyond impeachment can be a deciding factor in federal court cases when a party seeks to introduce “impeachment” evidence that was not otherwise provided in that party’s pretrial disclosures. See e.g., Stanley v. Edmonds-Leach, 783 F. 3d 1276, 1283 (D.C. Cir. 2015).