Amici states conduct the vast majority of criminal prosecutions in this country and therefore have a substantial interest in the integrity of those prosecutions. The question presented here asks whether a criminal defendant can strategically open the evidentiary curtain only partway, then use the Confrontation Clause to prevent his jury from seeing the additional evidence necessary to avoid creating a misleading impression of the facts, because the evidence that remains behind the curtain is testimonial hearsay. Amici states have a compelling interest in seeing that the Confrontation Clause remains a tool for discovering, not obscuring, truth.