Is a new trial required when an appellate court assumes a trial court's admission of irrelevant victim impact testimony was error?

QUESTIONS PRESENTED This Court ruled that, before a federal constitutional error can be deemed harmless, the prosecution must establish by proof beyond a reasonable doubt that the error was harmless. Chapman v. California, 386 U.S. 18, 24 (1967). In Payne v. Tennessee, 501 U.S. 808, 827-29 (1991), this Court addressed the admission of testimony concerning the victim’s background in the sentencing phase of a capital case. This Court has yet to address the admission of similar testimony in the trial phase of a capital case. This case presents this Court with that opportunity. After an appellate court assumes a trial court’s admission of irrelevant victim impact testimony was error, is it required to grant the defendant a new trial? When a court recognizes multiple constitutional violations and instances of erroneously admitted evidence, should it be required to assess the errors cumulatively before dismissing them all as harmless? i