In order to prove ineffective assistance of counsel under Strickland v. Washington, 466 U.S. 668 (1984), a defendant must prove by a preponderance of the evidence that his counsel’s representation fell below an objective standard of reasonableness, and there was a reasonable probability that the result of the proceedings would have been different but for counsel’s deficient performance. In Andrus v. Texas, Terence Andrus was convicted for killing two people during a carjacking when he was 20. During the sentencing phase, his counsel presented hardly any evidence of mitigating circumstances to the jury, and he was sentenced to death. During his habeas proceeding, a veritable “tidal wave” of mitigation evidence was revealed about Andrus’ abusive and dysfunctional childhood. The trial court found Andrus’ original counsel had been ineffective. The Texas Court of Criminal Appeals disagreed, writing without elaboration that Andrus had failed to meet his burden under Strickland.

The Court, in a 6-3 per curiam decision, reversed and remanded, holding that the evidence clearly showed Andrus received constitutionally deficient representation, and accused the Criminal Appeals court of having “failed to engage in any meaningful prejudice inquiry.” The majority required the state appellate court to take another look at the “tidal wave” of mitigating evidence to determine whether it would have had affected sentencing at his trial. Justice Alito, joined by Justices Thomas and Gorsuch, dissented, arguing that the Criminal Appeals court, by its own statement, did decide that the mitigating evidence would not have made any difference, and that there were plenty of aggravating factors in Andrus’ crime that would have overcome his mitigating evidence.

A link to the opinion is here: https://www.supremecourt.gov/opinions/19pdf/18-9674_2dp3.pdf